How to Inspect, Diagnose & Repair Oil Burners

OIL BURNER INSPECTION & REPAIR - How to Troubleshoot Problems at Oil Burners Found on Heating Boilers, Water Heaters, Furnaces
Questions & answers about oil burner inspection, diagnosis, & repair, troubleshooting procedure, how to get the oil burner running again, best order of diagnostic steps.
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How to inspect, diagnose & repair oil burners used on oil-fired heating boilers or furnaces using a visual inspection approach as well as (optional) simple test equipment. We include a description of common oil burner adjustment and operating problems and we illustrate some of the basic oil burner tests and measurements made in servicing and adjusting the equipment for safe, efficient operation. We illustrate oil burner smoke testing and oil burner carbon dioxide level measurement.

This website answers most questions about all types of heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors and students of heating service methods about common heating system defects. The articles at this website describe how to recognize common oil-fired heating appliance operating or safety defects, and how to save money on home heating costs

How to Troubleshoot Problems at Oil Burners Found on Heating Boilers, Water Heaters, Furnaces

This article explains the inspection, diagnosis, & repair of oil burners used in heating appliances such as hot water boilers, steam boilers, & water heaters.

If your heat is not working properly, and the problem does not seem to be the oil burner itself, see NO HEAT - BOILER or NO HEAT - FURNACE.

Readers needing an approach to heating system inspections that assures thoroughness, should also see HEATING SYSTEM INSPECTION PROCEDURE where we explain an organized approach to inspecting the entire heating system, beginning outdoors, continuing indoors, and ultimately in most detail in the boiler or furnace room. Also see CHIMNEY INSPECTION DIAGNOSIS REPAIR for details of chimney inspection, diagnosis, and repair.

In the oil burner inspection article provided Here we explain visual and other clues of oil burner problems.

An expert inspection of an oil burner begins either with having made note of building owner/occupant concerns (noises, odors, no heat, high fuel costs), or with having made some basic visual observations outside: a sooty chimney top, for example. The sketch is courtesy of Carson Dunlop Associates. )

The oil burner inspection continues indoors, even before entering the utility room where the oil burner (or often more than one of them if oil fuel is used for both heating and a separate water heater) is located: look at the building interior as you enter: are there odors, soot deposits, noises associated with the heating system?

The oil burner inspection becomes detailed, and diagnostic, when you can actually see the equipment. It's obvious that you should notice oil leaks, soot in the boiler or furnace room, noises, odors, signs of repeated repairs, piles of junked parts, signs of unprofessional work (covers off of controls, sloppy wiring or plumbing). But just what each of these clues might mean bears some additional explanation that we offer below.

Outdoor Clues of Heating Equipment Oil Burner Troubles

Heating company service tech rushing to leave the job (C) D Friedman

Was your heating service technician in a rush to leave? We took this photo of a heating service tech who was in a very big rush to leave the job, after his disastrous service call. We figured he was in over his head, or maybe had some personal troubles.

Fortunately the heating service company manager had other, excellent service technicians on staff who were able to un-botch this guy's job. The heating service tech really was smoking the tires of his service van - the photo was edited to remove the company name as the heating company actually provides excellent service, and except for this oddball who left a failed service call and ruts in the driveway.
How old is the building? Is it likely that older oil fired heating equipment is or was installed?
Where is the oil storage tank? Is it outdoors, subject to water, condensation, gelling? Let's not just blame the oil burner for problems if there are other issues at the property that can impact oil burner operation. Also see OIL TANKS and see OIL TANK PIPING & PIPING DEFECTS.
Soot at the chimney top of the flue used to vent oil fired equipment almost always indicates that the oil burner is or was operating poorly, producing smoky sooty exhaust. You might even see smoky exhaust if the oil burner is running while you are approaching the building. So take a look at the chimney(s) before you go indoors. Other trouble signs: short chimneys, missing chimney caps, or in the case of our heating service truck above, ruts in the yard and tire smoke in the air.
Signs of general poor home maintenance, or financial difficulties, can be clues that previous owners or occupants were just unable to tend to ordering and paying for regular heating system maintenance.

If the chimney top is sooty we don't yet know the cause of poor oil burner operation but we know there is a problem. If your inspection of the chimney top, even from ground level, perhaps with binoculars, shows water, frost, or mechanical damage to the chimney itself, or a missing chimney cap, these conditions may not only affect the operation of the oil burner, but they may be very unsafe. See CHIMNEY INSPECTION DIAGNOSIS REPAIR.

Indoor Clues of Oil Burner Troubles

On entering the building or by customer interview, start with a check for these signs of improper oil burner operation, regardless of whether the burner is powering a boiler, furnace, or water heater:

Are there noises when the oil burner is operating? Oil burner noises could be normal motor noise or could be a sign of serious and even dangerous heating system conditions - see both OIL BURNER NOISE SMOKE ODORS and OIL BURNER INSPECTION & REPAIR for details. Additional noises at the oil burner fuel unit (oil pump) are detailed at OIL BURNER FUEL UNIT.
Are there odors blamed on the oil burner or oil fired equipment? Odors may be from an oil leak, flue gas spillage, etc. See ODORS FROM HEATING SYSTEMS and see OIL BURNER NOISE SMOKE ODORS.
Is there soot visible in the living area or around the boiler or furnace room? Our photo at left makes clear that the oil burner has not been working properly and is blowing soot into the building.

See STAIN DIAGNOSIS on BUILDING INTERIORS, how to diagnose stains on walls, floors, carpets, and how to determine the stain source, be sure to see OIL BURNER SOOT & PUFFBACKS (photo at left), and OIL BURNER NOISE SMOKE ODORS, but also see THERMAL TRACKING & HEAT LOSS - because apparent "soot" on indoor surfaces may be simple house dust deposits caused by thermal tracking or thermal telegraphing.

More clues of trouble you can spot before getting close to the heating equipment itself are in our photos below.

Water damaged oil burner (C) Daniel Friedman

Are there signs of water leaks onto or into the oil burner, boiler, or furnace? As our house fire investigation photographs show (above/left), water passage down a chimney (say from a missing chimney cap) easily continue into the heating boiler or furnace where they may cause damage to the oil burner, boiler, furnace, or its controls.

Oil burner and boiler damaged from building fire: Notice those rust stains below the oil burner inspection port above and to the left of the burner tube? This oil fired heating boiler has been flooded. The photo at above left shows the probable passage of water entry, down the flue.

While the basement of this building was reported not to have contained substantial water (notice there are no flood lines on the outside of the heating boiler itself), water from above during extinguishment of a house fire ran down the chimney and flooded the boiler itself. Inspection and possibly repairs are needed before this equipment can be safely used.
Are there signs of heating oil leaks? an oil leak out of heating equipment also means air leaks into the oil system which almost certainly leads to improper operation and can lead to loss of heat or OIL BURNER SOOT & PUFFBACKS. Leaks can be anywhere from the oil tank to the oil burner, including the oil piping, fittings, filter, check valves, etc. See OIL TANK PIPING & PIPING DEFECTS. Heating oil leaks around the oil filter itself are detailed at OIL FILTERS on HEATING EQUIPMENT.

Signs of Trouble at the Oil Tank that Cause Oil Burner Problems

We mentioned outdoor oil tank problems above, but even indoors you may spot signs of trouble that affect oil burner operation.

An oil leak anywhere in the oil piping, are a problem, as we explained just above. A leak between the oil storage tank and the oil burner will usually cause improper oil burner operation - leaks of oil out of the oil piping become air leaks into the oil piping system when the oil burner is running and trying to draw oil from the oil storage tank, because during burner operation the oil piping is under vacuum.

Air leaks into the oil piping and burner cause improper oil burner shutdown, spewing unburned or only partially burned oil at oil burner shut-down, and risking dangerous (and sooty) puffbacks as well as telltale noises at oil burner start-up.
A leak into the oil tank itself or water accumulation from a bad oil delivery,or condensation can in the short run send water into the heating system piping and oil burner, leading to loss of heat and equipment damage. OIL TANK PIPING & PIPING DEFECTS.
A leaking heating oil tank, one that is leaking oil out, can lead to a costly oil spill cleanup. See OIL TANK LEAKS & SMELLS. But oil leaking out of the tank, if the leak is only in the out direction, won't cause oil burner problems. Instead it will increase your heating bill and contaminate the environment.

But watch out: depending on the location and nature of the leak, an oil tank leak out of the tank can, as oil levels in the tank drop, lead to water leaks into the oil tank - so you could have both problems.

Boiler or Furnace Room Clues of Oil Burner Troubles

Identify the heating system components in each building area. How old is the equipment, what are the signs that parts have been replaced (new transformer, new valves, new oil piping, new filters, new fuel units, discarded parts nearby).
Oil burner controls may themselves be a source of trouble - See CAD CELL RELAY SWITCH and Stack Relay Switch and also See AQUASTAT CONTROL Functions and THERMOSTATS. For oil fired warm air systems also see FAN LIMIT SWITCH control on heating furnaces. Controls for oil fired steam heating systems are discussed at Steam Heating Systems.
Look for damage to the furnace or boiler itself: if the boiler or furnace is old, cracked, rusted-through, leaking, damaged, repairing the oil burner may be the least of the owner's risks. And if the boiler, furnace, or water heater is unsafe or needs immediate repair or replacement, fixing the oil burner and leaving the job is dangerous.

Our photo (left) shows a furnace that should not be used, and needs immediate replacement. Fixing its oil burner, or even inspecting it would be foolish - this furnace should be left shut down, red-tagged, and appropriate oral and written warnings issued. If the furnace, boiler, or water heater has had a safety recall, that's critical information for the owners to know about. For example, see Blueray Heating Boilers/Furnaces Safety Recall by the US CPSC, with additional history, photos, and technical details.
Look at the heating equipment's service tag: has the equipment been serviced annually; are there records of other no-heat service calls - often a good service tech will note on the service tag the no-heat call, the diagnosis, and what parts were replaced. At Heating Cost Reduction Advice: How to Save on Home Heating Costs, we discuss heating tuneup tips for oil burners to reduce heating cost.

Audel guide to oil burner efficiency (C) Daniel Friedman - Audel

Oil fired equipment efficiency measurements: If you do not see a small (roughly 1/4" diameter) hole in the flue vent connector just above the boiler, before the barometric damper, then this heating equipment has never been properly tuned and measured for proper operation.

While it was possible to "eyeball" older oil fired equipment (spit on the flue for temperature and blow cigarette smoke at the burner for draft), modern oil fired equipment requires more accurate measurement and adjustment for good operation.

As our sketch from the Audel Oil Burner Guide shows, measuring the stack temperature and CO₂ level gives a critical indication of the heating system efficiency, in other words, measuring what percent of each dollar spent on heating oil is going up the chimney versus into the building as heat.

The Guide also includes this chart of oil fired heating system efficiency at different CO₂ levels and stack temperatures.

Oil burner stack temperature measurement (C) D Friedman

The little hole we describe is where the service tech inserts test equipment to measure stack temperature, smoke level, and CO level. Some tech's use two holes to permit more than one measurement simultaneously. No hole = never measured. (Or new flue vent connector parts have just been installed on older equipment and no one has made a hole yet.)

Details about this procedure for measuring oil burner efficiency are at Oil Burner CO₂ Test.

Our photo (left) shows a Bachrach stack temperature measurement being made "in the breech" above a troublesome oil burner and boiler installation.

Watch out: don't record the stack temperature before the oil-fired heating system has been running for five minutes or so - you want to be sure the system has reached its stable and "normal" operating temperature.

Waiting a few minutes at this boiler we saw the flue temperature rise to 600 degF. At 600 degF. this heating system was left running a bit "hot" by the service tech. Why? Because a too-short chimney meant the system had a history of inadequate draft, sooting, backpressure, puffbacks, and loss of heat. This "fix" was a band-aid that kept the system running longer between (frequent) service calls, but at the expense of higher heating bills and wasted fuel.

We could have addressed this short chimney with a draft inducer fan, but a taller flue would be smart anyway, to get the chimney top higher than the roof surface. We discuss examples of extending chimney height to improve draft, performance, and fire safety separately at Chimney Height Extensions. We discuss draft inducer or "draft boosting" fans for heating systems (and maybe for some fireplaces) in detail at Draft Inducer Fans.

Just how short is "too short" for a chimney is a problem along with roof clearance requirements discussed at Chimney Height & Clearance

At the heating boiler or furnace, identify the fuel source and follow fuel supply piping to its source (an oil tank, LP gas tank, or gas meter, for example) - you may spot the oil leaks and piping problems we mentioned above.
Look at the oil burner combustion air supply - it's remarkable how often the oil burner service tech tunes up the system with the door to the boiler or furnace room open (who wants to work in a little closet), then leaves, closing the door, and shutting off the only combustion air supply to the equipment - a likely cause of sooty operation and other troubles. See COMBUSTION AIR DEFECTS.

Barometric damper inspection (C) Daniel Friedman

Look at the furnace or boiler connection to the chimney - the flue vent connector, barometric damper, and for signs of trouble with the chimney itself (no cleanout door, air leaks, blocked flue).

See CHIMNEY INSPECTION DIAGNOSIS REPAIR for the chimney itself, and see Flue Vent Connectors - Boilers, Furnaces for a discussion of flue vent connectors, signs of blocked flues, dead end chimney hazards, and other venting defects that can cause oil burner operating problems.
Look at and look into the barometric damper or draft regulator: is there one installed, is it properly installed, is the flue thick with soot, is soot blowing out of the draft regulator?

Our photo, left, shows so much debris in the breech of this oil fired heater that the oil burner is likely to see trouble itself.
See DRAFT REGULATORS, DAMPERS, BOOSTERS for details. A discussion of this particular photo and those rusty sooty fragments in view is found at How to Inspect a Barometric Damper.

Signs of Trouble at the Oil Burner Itself - Visual Inspection

Oil burner backpressure (C) Daniel Friedman

Are there signs of backpressure in the combustion chamber? The cause may be a dirty boiler or furnace, a blocked flue, inadequate draft, etc.

We have seen oil burners that suffered through three or four transformer replacements, in one job every few months: the service tech had not realized that chimney problems and backpressure were causing so much heat blow-back into the oil burner tube that the transformers were being "cooked" - the clue was obvious if you knew that tarry goop leaking out of a transformer means it's overheating.

Our photo of backpressure burns at an oil fired boiler (left) shows rust around the inspection port - a hot combustion chamber has burned off the paint in this area.

The oil burner itself, a Beckett oil burner, was tolerating the backpressure in this case and was undamaged. But the backpressure cause (a dirty boiler) needed to be addressed. More often we see soot around the oil burner as a sign of backpressure, such as this horizontal furnace oil fired unit backpressure photo.

Are there oil leaks at the oil burner or at the Fire-o-matic fusible link oil valve (that should be installed at the oil burner burner) or at the oil tank? See OIL LINE SAFETY VALVES. Also see OIL TANK PIPING & PIPING DEFECTS.
Is the system safely connected to a chimney? If not, stop worrying about the oil burner and shut the system down.
Look at the temperature/pressure gauge: normal operating values? Boiler temperature and pressure are indicated on the TP gauge and should show increase not to exceed normal operating limits (200 deg F or less and less than 30 psi) - Gauges on Heating Equipment.

If the aquastat settings controlling a hot water heating system boiler are set to unusual temperatures that may indicate an operating problem, a heat distribution problem, an un-trained service tech, or homeowner meddling. On hot water heating boilers, the pressure and temperature gauge reads about 12 psi cold, less than 30 psi hot. Over 30 psi the temperature will cause spillage at the temperature/pressure relief valve.
Typical operating temperature settings on the oil burner primary control: LO-120-160 HI-180-200 degF.

Typical operating temperature observed at the gauge will be below the high, and can be as low as nighttime room temperature in non-heating season if no tankless coil is in use. The temperature/pressure gauge may help in checking for normal conditions before and during boiler operation. However the gauge can be wrong! - Gauges on Heating Equipment

Furnace temperatures on oil burner-fired warm air heating systems are not normally measured by a gauge but are reflected on the settings of the FAN LIMIT SWITCH.

Steam boilers and their oil burners in most residential installations operate at low pressure (a fraction of 1 psi) - if the steam boiler pressure switch is set high, that may indicate a heat distribution problem that has been "fixed" using an expedient but improper approach. (See Steam Heating Systems).

Oil burners on water heaters use similar (but generally simpler) high limit and low limit temperature controls but a temperature/press rue relief valve that is designed for water heater operating temperatures and pressures.
Water leaks at valves or fittings which drip into the jacket of a steel boiler or onto controls or zone valves or for warm air systems, plumbing leaks onto the furnace, or condensate leaks from a combination heating and air conditioning system that drip onto the heat exchanger risk failure, dangerous carbon monoxide gas hazards, and ultimately loss of heat.

Oil burner fuel unit air bleed valve (C) Daniel Friedman

Oil burner air shutter (photo above right) debris, dirt, or shutter adjustment problems or inadequate combustion air; because there is invariably a thin oil film on these parts, building pets, especially dogs and cats, may shed hair that collects-on and blocks combustion air entering the oil burner.

Our photo (above right) shows our pen (photo above right, at bottom center) pointing to the very small opening in the air shutter at this Beckett oil burner. You can see that even a small amount of cat hair sticking on this opening will easily block the flow of combustion air into the oil burner, thus causing improper (and sooty) oil burner operation. In this photo the opening is not blocked by debris, though we see a little soot there.
Oil leaks at air bleed valves (photo above left) or other fittings on the fuel unit on the oil burner. In our photo (above left) our pen points to the bleeder valve used to purge air from the oil line; Look for oil drips here as well as at the oil line fittings (and look at the fittings and gaskets and connections on the OIL PUMP FUEL UNIT (photo above left).

Signs of Trouble at the Oil Burner - During Operation

See Boiler Operation Details, 39 steps in how a heating boiler works. The following oil burner noise clues are taken from our more complete article: OIL BURNER NOISE SMOKE ODORS. Also see COMPLETE COMBUSTION, Stoichiometric for an explanation of complete fuel combustion and boiler or furnace maximum efficiency.

Watch out: Do you see some reason not to turn this oil burner system on? A flooded combustion chamber is a reason not to light off the oil burner, at risk of a puffback. See SAFETY, HEATING INSPECTION.
Furnace noises of shrieks, whining, or grinding coming from the electric motor or blower assembly of a furnace air handler probably mean that the system has a bad bearing (or fan belt) and prompt repair service is needed. It's best to shut down such a system since certain failures, such as sucking a furnace filter into the blower assembly, can lead to overheating and cause a fire.
Noises & soot buildup can lead to a potentially dangerous puffback which can damage the heating equipment and blow soot and smoke throughout the building. An experienced heating service technician may recognize the following diagnostic list of heating system or oil burner noises as well as perhaps other signs of trouble:
Noises during oil burner startup - a "bang" or puffback which blows soot into the room through the barometric damper or through other equipment openings: the oil pump may not be shutting down properly at the end of an oil burn cycle, leaking incompletely burned oil into the combustion chamber. That oil ignites at startup causing a potentially dangerous puffback. Immediate service and repair are needed.
Noises during oil burner startup - a "rumbling" sound (which usually continues all during operation" or a "stumbling" sound in the combustion chamber probably indicates that the system needs inspection and cleaning very soon. Some noise is normal however, but the normal sounds tend to be more smooth and continuous.
Noises during oil burner shut-down - a stumbling or rumbling after the oil burner motor has stopped, indicate that oil is continuing to leak into the combustion chamber and risks a dangerous puffback - see "Noises during oil burner startup" above. Immediate service is recommended.
Oil burner noises of shrieks or grinding coming from the electric motor or oil pump on the oil burner mean that immediate service is needed - probably a bearing is failing. Also see Table C: 7 Things to Check if an Electric Motor is Noisy
Oil burner electric motor off on reset or oil burner motor won't run: if the reset switch on the electric motor that drives the oil burner keeps going off (See ELECTRIC MOTOR DIAGNOSTIC GUIDE and see RESET SWITCH - ELECTRIC MOTOR) you'll need help from a trained service technician to determine the problem.

Oil Burner Smoke Test - Indicates Proper Combustion Air, Draft, Burner Adjustment

The basic measurements made by any competent oil heat service technician include the stack temperature, draft, smoke level, and carbon dioxide level. These data tell us whether or not the equipment is properly adjusted and operating safely and economically.

One of these most basic tests performed by an oil heat service technician is the "smoke test" using a strip of filter paper and a pump to sample the oil burner exhaust, measuring the level of smoke in the exhaust.

Our photo (left) shows a traditional smoke testing pump (the black cylinder with a handle at its right end) used for decades. This equipment was produced by Bachrach, an oil burner test equipment manufacturer.

The technician allows the oil burner to reach normal operating temperature (perhaps after it has been on for five minutes),
A clean white strip of filter paper is inserted into the end of the smoke testing pump.
The nozzle of the smoke tester is inserted into a 1/4" diameter hole in the flue vent connector pipe, typically just a few inches above the top of the oil-fired heating boiler or furnace.
The pump is operated
The filter strip is removed and the "blackness" of the sample spot is compared with a scale that rates the soot level. An experienced oil heat service technician simply looks at the black or gray spot on the filter paper.

Zero-level smoke is actually "too clean" for most oil burners, and means that there is too much air entering the oil burner, causing the burner to operate too hot, and sending too much heat (and thus the money the homeowner spent on heating oil) up the chimney.

A smoke level of "1" or "2" is normal. In our oil burner smoke test results photo (at left) you can see four smoke test samples. #1 is certainly too dirty, #'s 2 and 3 are a bit high, though we might accept sample #3. Sample #4 is just slightly above zero and is a good setting. [Click any image or table to see an enlarged, detailed version.]

Higher smoke levels indicate that the system is operating too "dirty" or smoky. High levels of soot in the oil burner exhaust mean that the system will deposit soot more rapidly inside of the furnace or boiler heat exchanger, interfering with heat transfer into the building heating air or water, and thus increasing system operating cost - meaning higher heating bills and more frequent oil burner service needed.

Very high smoke levels may indicate or even cause plugging up of the furnace or boiler, leading to improper oil burner operation, an unsafe system, and possibly other malfunctions, even a "puffback".

Oil Burner CO₂ Test - Carbon Dioxide Level Indicates System Efficiency

The second common test performed by an oil heat technician evaluates the oil burner efficiency by measuring the carbon dioxide level or CO₂ level in the oil burner exhaust. While there are electronic sensors used by some technicians for this purpose, many oil heat service tech's continue to use the time-tested Bachrach Fyrite™ oil burner tester shown below.

Oil burner smoke test equipment, Bachrach Kit (C) Daniel Friedman

Bachrach carbon dioxide test for oil burners (C) Daniel Friedman

Our photos above show the rubber bulb and tubing used to pump oil burner exhaust gases into the CO₂ level tester (the bulb and tubing atop the smoke tester, above left), and a closeup of a well-used CO₂ tester (above right).

Measurement is made at the same flue vent connector location as we discussed above.

In fact when the author (DF) attended oil burner school we were taught to make two openings into the flue so that smoke level and CO₂ measurements could be made through one opening while a thermometer or draft gauge monitored those two additional data points at the second opening.

The CO₂ tester is filled with a red fluid that changes volume in response to carbon dioxide level. The Fyrite test unit is inverted, returned to upright, tilted at 45 degrees, to prepare it for use and to calibrate or set the "zero point" on the CO₂ gauge. A cap on the unit is depressed to vent the unit to the atmosphere and the zero point is set on the adjustable gauge.
Exhaust gas is pumped into the CO₂ tester, the tester is treated with flue gas exhaust for the required number of strokes (18) to purge the tubing and bulb and analyzer (tester). The analyzer is inverted, then returned to upright, tilted 45 degrees, returned to upright, and the CO₂ scale is read.

The Carbon Dioxide vs Oil Burner Efficiency chart below explains how the percent of carbon dioxide in oil burner exhaust gases translates into oil burner efficiency. Bachrach Fyrite instructions and Oil Burner efficiency chart below, source: Audel's Oil Burner Guide.

[Click any image or table to see an enlarged, detailed version.]

Signs of Trouble Inside the Oil Burner - Simple Disassembly, Inspection, Testing

Oil burner gun operation (C) D Friedman - Audel

We look for obvious trouble signs before making any changes or adjustments to the oil burner assembly by turning off power to the equipment, shutting off the oil supply line at the closest service valve, and opening the oil burner for inspection.

Our sketch (left) shows how an oil burner gun atomizes and sprays heating oil into the combustion chamber - Audel Oil Burner Guide

Most oil burners are opened by loosening two screw clamps at the front of the transformer box mounted atop the oil burner tube and folding the hinged transformer back to expose the interior of the tube, the oil burner nozzle assembly, and other parts. Some obvious trouble signs inside the oil burner include:

Cad cell sensor sooty or dirty (probably from backpressure in the combustion chamber combined with sooty operation - can force an oil burner to remain "off on reset" when the cadmium cell sensor that informs the safety control cannot sense that a flame is present. See CAD CELL RELAY SWITCH for details and also see Reset Switch - Primary Control.
Cracked, damaged ceramic electrode insulators on the oil burner assembly - a short here will cause improper ignition
Dirty turbulator assembly (if present) mounted on the end of the oil burner nozzle - can interfere with proper air flow around the nozzle and thus with proper heating oil combustion. The turbulator is a fan-like collection of fins that is mounted, usually on the end of the oil burner nozzle by a bracket, and that provides increased air turbulence to improve heating oil atomization and spray pattern, thus improving combustion efficiency. Debris and soot can block the air space between the turbulator blades, causing this device to stop working, and leading to dirty sooty oil burner operation.
Dirty oil burner nozzle, especially crud build-up that is blocking oil flow or shorting out the oil burner nozzle electrodes - see OIL BURNER NOZZLE & ELECTRODES

Loose, damaged, misaligned oil burner electrodes (use a simple oil burner nozzle gauge or a small steel rule to see that the position of the oil burner electrodes in their gap apart, their distance above the oil burner nozzle orifice, and their distance forward or backwards relative to the face of the oil burner nozzle are according to the manufacturer's specification. See OIL BURNER NOZZLE & ELECTRODES for details.

Leaky shaft at the oil burner fuel unit (C) Daniel Friedman

Damaged squirrel cage blower assembly - loose, wobbly bearings, bent fins, dirt and debris; this problem will reduce combustion air input to the oil burner and will result in poor, sooty operation.
Damaged coupling joining the electric motor that drives the oil burner, the combustion air blower squirrel cage fan, and the shaft that turns the fuel pump unit itself.

In our photo, we see tarry goop around the fuel unit drive shaft - a fuel unit drive shaft oil leak discussed at OIL BURNER FUEL UNIT. Even a small leak in this location can lead to loss of combustion air and improper burner operation.
Oil and debris inside the oil burner tube - possible leaks, incomplete combustion, improperly mounted oil burner gun assembly
Overheating inside the oil burner tube, tarry goop leaking out of the transformer assembly

Oil Burner Won't Run: Diagnostic Steps - what to check in what order

We have collected oil burner diagnostic procedures from several texts, ^{[1] - [22]} adapted, expanded, and generally re-ordered steps in order of most likely to be successful and easiest to perform. For example it makes sense to check for a valve or switch that is off, or an oil filter that is clogged, before we start disassembling the fuel unit.

Oil burner won't start - HEAT WON'T TURN ON

Make a quick visual check for:
- Power switched off to the unit - ELECTRICAL POWER SWITCH FOR HEAT
- A fuse or circuit breaker or fusible switch has blown
- Adequate oil supply in the oil tank - OIL TANK GAUGES
- The oil supply valves are all open - OIL LINE QUICK STOP VALVES & OIL LINE SAFETY VALVES
- The thermostat is really calling for heat - it is switched to "heat" and proper time of day
- The room temperature is below the thermostat set temperature - THERMOSTATS, HEATING / COOLING
- Evidence of an oil-flooded combustion chamber (you do not want to try turning on the burner in this condition as there is danger of a horrible puffback mess)
Is there electrical power? First: test for voltage across terminals 1 & 2 at the stack relay or cad cell relay primary control

No voltage,
- Check the LIMIT SWITCH, BOILER,check the Reset Switch - Heater Primary Control, check the LOW WATER CUTOFF VALVE (if it's hot water heat or steam heat), check any fusible switches, find and check all of the electrical switches that can turn off the unit (the stair switch, the service switch, the breaker or fuse in the panel - ELECTRICAL POWER SWITCH FOR HEAT).
- VOLTS / AMPS MEASUREMENT EQUIP
Voltage present, next, jump across the thermostat terminals.
- The burner relay pulls in and
  - The oil burner fires up
    - Check the flame for normal appearance, remove your thermostat jumper and make sure the thermostat calls for heat. The system seemed to run OK when you jumped the TT terminals, right? With your thermostat jumper removed:
      - If the burner does not again go off on reset or "lock out" then
        
        Check for short on-cycling of the oil burner. This condition can lead to off on reset.
        
        Not short cycling - the system should be OK
        
        Oil Burner System short cycles:
        
        Check for loose wires at controls, power, thermostats &c.
        
        Check for hot or burned relay switch contacts,
        
        Check for thermostat bounce or thermostat internal wiring or flat cable connection defects - THERMOSTATS, HEATING / COOLING
        
        Check the aquastat HI, LO and DIFF settings - AQUASTAT CONTROL
        
        Check also for improper voltage.
        
        Check the low water cutoff switch (that can also bounce) if one is present - LOW WATER CUTOFF VALVE
        
        Check for improperly-set heat anticipator - HEAT ANTICIPATOR Adjustment (if present) or
        
        Check for improperly set HVAC cycle or swing temperature variation - THERMOSTAT SWITCHES, INTERNAL
        
        If all of these look ok you may need to change the primary control relay.
        
        Thanks to HVAC tech Anthony Alaggio for suggestions about oil burner short cycling.
      - If the burner oil burner does not fire up, there is a problem with the thermostat or the 24V thermostat circuit. You may need to change the 24V transformer or the thermostat.
      - If the burner fires up but goes off on reset again,
        
        Check for a bad flame, bad firing, dirty nozzle, electrodes, oil leak at the nozzle adapter, blocked combustion air
        
        If a stack relay is used, check for a dirty or broken helix
        
        If a cad cell relay is used, check for a dirty or failed cad cell eye
        
        If these look OK you probably have to change the primary control relay
  - The oil burner does not fire up successfully
    - If the burner motor started, check for
      - No oil flow comes out of the burner. You already checked that there is really oil in the tank, right? - OIL TANK GAUGES
        
        Check that the oil tank float gauge is not stuck.
        
        Check for a dirty or clogged oil filter - OIL FILTERS on HEATING EQUIPMENT
        
        Check for a dirty, clogged oil burner nozzle - Oil Burner Nozzles [PDF]
        
        Bleed the fuel unit of any trapped air, then check the pressure (pressure out, vacuum in) on the oil lines.
        
        Check any oil safety valves, check valves, PRVs, OIL LINE SAFETY VALVES
        
        Check for a clogged strainer in the oil burner fuel unit
        
        Check that the burner motor is turning the burner blower and fuel unit (a bad coupling or a bad motor)
        
        Check for an oil line that is clogged or blocked by ice (outdoor tank) or sludge - a clue is to see how much crud is in the bottom of the oil filter canister. OIL LINE CLOGGING FIX
        
        If there is oil flowing freely at the oil line and all of the above check out, we suspect that the fuel unit is not pumping.
      - No ignition: oil comes out of the nozzle but there is no ignition. Check
        
        Check for voltage at the primary, terminals 2/4 or if constant ignition 2/3
        
        Test the ignition transformer for spark (old timers know a screwdriver trick; if the flame is blue and reaches mostly across the gap of the transformer springs the transformer is probably ok. If the transformer is weak the spark will be dead, not bridge the gap to the screwdriver, or not extend to at least 3/4 the width between the contact springs, or will be orange not blue in color.
        
        If the transformer does not check out, replace it.
        
        If the transformer looks OK check closely the ignition leads including for cracked shorting ceramic insulators in the burner assembly or an improper or improper gap or damaged electrodes. You already looked to be sure the electrodes were not bridged with soot and crud, right?
    - If the burner motor does not start, check for
      - check primary terminals 2/3
      - check for live voltage at wires powering the motor (if no power there and the relay pulled then there may be a broken wire)
      - If hot and ground are good at the motor, check for a thermal overload switch pop on the motor - if it's out, let the motor cool, reset it and start again. RESET SWITCH - ELECTRIC MOTOR
      - If after reset of the thermal overload the motor still won't start, replace the motor.
      - At ELECTRIC MOTOR DIAGNOSTIC GUIDE we describe both offline and online electric motor circuit analysis (MCA) test procedures.
- If the relay does not pull in,
  - if it's a stack relay, re-step the relay contacts inside the control. Reset Switch - Stack Relays
  - Check the lock switch - Reset Switch - Heater Primary Control
  - Check for cold relay points - broken, not connected
  - check for a broken or clogged helix in the stack relay
  - check for a bad cad cell relay

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Anthony Alaggio can be contacted through Bottini Fuel (Hudson Valley, NY) or directly for HVAC service at 914-489-0632. Email: crackin95vtec@yahoo.com Special thanks to Mr. Alaggio, an HVAC service technician for technical suggestions regarding oil heat troubleshooting & more causes of oil burner short-cycling 4/12/2013.
[1] Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted a Home Inspection Home Study Course, and publications such as the Home Reference Book, the Home Reference eBook, and report writing materials including the Horizon report writer, and home inspect ion services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
[2] Beckett Corporation, 38251 Center Ridge Rd., North Ridgeville, OH 44039 440-327-1060 Email: sales@beckettcorp.com supplies residential and commercial oil burners for boilers, furnaces, and water heaters - see www.beckettcorp.com/
[3] Audels Oil Burner Guide, Installation, Servicing, Repairing, Frank D. Graham, 1940's edition (obsolete). Updated versions of this guide are available in various editions, 1947, 1950, 1955, 1958, 1959, 1962, 1965, 1967, and at prices from around $3.00 to nearly $70.00 - useful for simple, clear, but not current, explanation of how heating equipment works. The original retail price was $1.00. Used copies are available at Amazon.com
[4] A Total Look at Oil Burner Nozzles, available from Delavan Fuel Metering Products, a reference guide for oil burner service technicians, Delavan Spray Technologies, Fuel Metering Products Division, PO Box 969, Bamberg SC 29003, Tel: 800-982-6943 or 803-245-4347, ( Delavan is a division of BF Goodrich); web search 12/30/2010, original source: http://www.delavaninc.com/pdf/total_look.pdf
Note & disclosure: when we (DF) were servicing oil burner equipment, Delavan nozzles gave us such excellent results, especially using hollow cone spray patterns in solving combustion problems, that this brand was our standard stock-item on our truck. Other brands of oil burner nozzles are of course also of excellent quality. It is the proper matching of nozzle size and type and spray pattern to the equipment that is critical.
[5] Fuel Nozzles for Oil Burners, Technical Aspects of Applications, E. O. Olson, Chief Engineer (deceased)
Delavan Fuel Metering Products Operation, Bamberg, South Carolina, Delavan Fuel Metering Products, a reference guide for oil burner service technicians, Delavan Spray Technologies, Fuel Metering Products Division, PO Box 969, Bamberg SC 29003, Tel: 800-982-6943 or 803-245-4347, ( Delavan is a division of BF Goodrich); web search 12/30/2010, original source: http://www.delavaninc.com/pdf/Fuel_Nozzles_for_Burners.PDF
[6] Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
[7] The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
[8] Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
[9] The Lost Art of Steam Heating, John Doe [Dan Holohan], 516-579-3046 FAX, at Amazon.com and the InspectAPedia bookstore
[10] Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
[11] Principles of Home Inspection: Steam, Electric & Wall/Floor Heating, Carson Dunlop, at Amazon.com and the InspectAPedia bookstore
[12] "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[13] "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[14] "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
[15] Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
[16] Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
[17] Installation Guide for Residential Hydronic Heating Systems
[18] Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
[19] Crown Serviceman's Handbook: Ignition Electrode Assemblies, Terminals and Cable, Tools and Accessories, Crown Engineering Corporation, Marlboro, NJ 07746 [1986]. This publication includes oil burner troubleshooting diagnostic suggestions reprinted with permission of Fuel Oil & Oil Heat Magazine.
[21] The Wholesaler's & Installer's Guide to OEM Oil Specifications, R.W. Beckett Corporation, PO Box 1289, Elyria, OH 44036, 216-327-1060 [1988] This publication gives the model, burner type, air tube combination, head type, static plat dimensions, blower wheel dimensions, and oil burner nozzle type for just about ever manufacturer and model of oil fired heating equipment including Addison Products, Axeman-Anderson, Bard Manufacturing, BDP, Borg-Warner, Boyertown Furnace, Burnham, Carrier Corp., Clare Brothers, Columbia Boiler Co., Crown Industries, Dornback Furnace, Ducane, Dunkirk Radiator, Duo-Matic/Olsen, Electric Furnace-Man, Ener Royal Technology, Energy Kinetics, Everhot All-Corporation, F.P. Industry, Fraser-Johnston, Heat Controller, Hydrotherm Inc., Johnson Corp., Lochinvar, Logwood-Marathon Heater, Inc., Longwood Furnace Corp., Luxaire, Magic Chef, Melvin Manufacturing Corp., Metromatic Mfg. Co., Miller Heating & A/C, Modine Manufacturing, Newmac Manufacturing, New Yorker, Oneida Heater, Peerless Heater, Perfection Products, Pow-R-Matic, Inc., Reznor, Rheem Manufacturing, Ruud, Slant/Fin, H.B. Smith, State Industries, Tekton Corp., Teledyne Laars, Thermo Dynamics, Thermo Products, Trianco, Inc., Ultimate Eng., Utica Boiler, Vallant, Van Wert Manufacturing, Weil-Mclain, Williamson Co., Wise, Inc., XXth Century. But believe it or not this is not the whole list of manufacturers from the 1970's and 1980's. Reference [22] below includes a still longer list.
[22] Steinen's [Oil Burner] Nozzle Guide, Oil burner nozzle specifications, draft regulators, nozzle filters, flame mirrors, oil burner nozzle kits, nozzle racks, nozzle extractors, nozzle adapters. Wm. Steinen Mfg. Co., 29 East Halsey Rd., Parsippany NJ 07054, Tel: 201-887-6400 [1970].
[22] Burnham Heating Helper, [heating system design & layout in a mini booklet], Burnham Corporation, PO Box 3089, Lancaster PA 17603, Tel: 717-481-8400, 9th printing, 7/01

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson, Dunlop & Associates Ltd., Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^®^{author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.}

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
Audels Oil Burner Guide, Installation, Servicing, Repairing, Frank D. Graham, 1940's edition (obsolete). Updated versions of this guide are available in various editions, 1947, 1950, 1955, 1958, 1959, 1962, 1965, 1967, and at prices from around $3.00 to nearly $70.00 - useful for simple, clear, but not current, explanation of how heating equipment works. The original retail price was $1.00. Used copies are available at Amazon.com
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
The Lost Art of Steam Heating, John Doe [Dan Holohan], 516-579-3046 FAX, at Amazon.com and the InspectAPedia bookstore
Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
Principles of Home Inspection: Steam, Electric & Wall/Floor Heating, Carson Dunlop, at Amazon.com and the InspectAPedia bookstore
"Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Can X-Ray Vision Warn of Sink Holes? in Florida or elsewhere
Developing your X-Ray Vision - 6th Ed. The Science of Building Inspections - advanced home inspection techniques including "The Limits of Vision," "Inattentional Blindness," "Invasive Inspection Methods," "Missed Defects," & "Contextual Inspection," "Termite Inspections," "Moisture & Building Water Entry," © Daniel Friedman 2006-1987
The Nature of Vision, Inspecting Complex Systems,why inspectors don't see certain defects and miss important omissions
...


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