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Heating boiler inspection: This document presents the detailed sequence of steps to use when inspecting residential heating systems with focus on heating boilers and furnaces, on assuring
completeness, accuracy, and on maximum heating system defect detection. The heating system inspection methodology involved is intended to be generalized to
the forensic diagnostic inspection of any complex system in order to have the highest probability of detecting
important safety or operating defects.
This sounds fancier than intended. Our object is to use an organized
procedure for inspecting for defects, without losing the ability to discover unexpected problems as well. The methodology discussed includes both details specific to heating boilers (the full outline at "Contents")
and more general complex-system inspection methods (listed immediately below).
Detailed Steps in the Sequence of Examination of Oil-Fired Hot Water Boilers
Viewpoint #4--Detailed close scrutiny of the equipment, after a few "sanity checks" ASHI 9.1.A.1 The inspector shall observe ... heating equipment
Inspect before operating the boiler
What are we looking at? Form a working Definition: A system
which heats the house. A steel, copper, or cast iron "box"
of hot water, connected to a loop of pipe (and radiators or baseboards)
which runs around through the living area. The same physical water
stays in the boiler and is circulated by a pump so that heat is delivered
to the living area. Burning oil makes hot gases which are used to
heat the water before being exhausted outside. Pumps move fluids.
Safety controls at various points protect against a number of potential
We include links to detailed heating system articles that explain how boiler or furnace parts and components work, how to inspect or repair them, and description of common problems that occur with each heating system component.
Look at the temperature/pressure gauge: normal operating values?
Look for leaks in the boiler itself (Cast iron is more resistant to death by leaks than steel. Older cast iron systems without
tankless coils, if shut off in summer, may be at risk of leakage and hidden damage. Steel rusts through. Cast iron cracks or leaks at joints.)
Look for leaks at controls now and again in the sequence below
Leaks at valves or fittings which drip into the jacket of a steel boiler or onto controls or zone valves risk failure and
loss of heat.
Is there a tankless coil? If so, address both topics, looking at heating first, DHW second.
Examine components in the sequence of operation
Training in proper operation sequence of the equipment and in the
function of its controls is a step towards technical correctness. If you do not understand how a mechanical system works you cannot
reliably expect to observe missing or defective components. This discussion is an exercise using sequence of operation to work
for completeness. It is not technically exhaustive, it focuses on
a specific example: oil-fired hot water, zoned, heating system.
Examine the accessible parts of the system. Let your eye travel
from component to component in the sequence of operation. Apply the
inspection logic discussed earlier, at each step. Consider the implications
should each component be missing, damaged, inoperative, leaky, noisy,
sooty, repaired by an amateur, etc. Think through the operating sequence as you examine each component in that
The following are the steps in one common set-up. This list is lengthy
and detailed. The actual visual examination may take only a few minutes.
room thermostat switches on ASHI 9.1.A.2 normal operating controls - see THERMOSTATS
[zone valve opens and] circulator [starts] [except in Canada where circulators may be set up to run continuously and where the thermostat directly turns on the oil burner] [Circulator usually located on cooler return-side of the distribution piping loop-longer life.] - ZONE VALVES, HEATING
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
hot heating water leaves boiler passing by the ...
air scoop (not always present; avoids air-bound baseboards)
[air purge] (not always present; often leaky or sealed off)
[automatic] water feeder (normally the manual valve for water supply to boiler is "on", the automatic valve is closed unless the boiler pressure drops below 12-15 psi. This valve is often also a backflow-preventer.) - WATER FEEDER VALVES, HYDRONIC BOILER
expansion tank (waterlogged, dumping relief valve)(attic? no r v?=some old equipment) - EXPANSION TANKS
[zone valve] (not always used, shorter life on the "hot" supply side of <->piping) - ZONE VALVES, HEATING
distribution piping (watch for mineral salts indicating small clogged leaks)
baseboards - which warm the room and thus the ... ASHI 9.1.A.6 heat distribution systems including fans, pumps, ducts and piping with supports, dampers, insulation, air filters, registers, radiators, fan-coil units, convectors - RADIATORS and AIR BLEEDER VALVES
room thermostat senses the heat increase. Water passes - THERMOSTATS
hot gases pass through tubes in steel or between sections in cast iron boiler, sending heat back into the heating water through the heat exchanger. (soot acts as insulation--boiler cleaned recently?)
hot gases are collected at top of boiler and sent out through exhaust flue ...
where the barometric damper assures proper and even draft; hot gases continue ..., up
up the chimney to outdoors. ASHI 9.1.A.4 chimneys, flues, and vents (is the chimney improperly shared or vented to multiple floors?) ASHI 9.1.A.5 solid fuel heating devices [e.g. wood and coal stoves]
boiler temperature rises up to the "HI" limit. (Thinking of High take a look for a pressure relief valve and look for defects there: leaking, corroded, not piped to floor, reduced diameter piping.) - RELIEF VALVE, TP VALVE, BOILER
sensor informs Primary Control which turns off the burner-(sloppy shut down?) (Circulator is continuing to run)
the room is warm enough according to the thermostat so the ...
thermostat senses the temperature rise and opens its switch. (Special thermostat sophistication and functions excluded here)
Pressure and Temperature gauge--12 psi cold, less than 30 psi hot. Over 30 psi dumps relief valve.(Typical operating temperature
settings LO-120-160 HI-180-200 °F. 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
Tankless coil--leaks, missing mixing/tempering valve, relief valve (some jurisdictions). Risk of scalding water at the house sinks/tubs if there is no mixing valve. - TANKLESS COILS
Leaks and Corrosion - some implications
Surface rust--repairable. Clean when serviced and monitor
Exfoliation--very serious, possibly not repairable,
risks loss of boiler.
Common Heating System Leak Locations
Coil mounting plate - see rust stains below and around plate
Pipe fittings at face of coil plate - mineral salts
Leaks around bolt openings - suspect hidden damage
Examples of understanding function and implications:
Leaks are never acceptable, anywhere on a heating system. Leaking relief valves
need immediate attention and repair (Leaking relief valve could be
due to water-logged expansion tank, improper control settings (temp
too high), improper automatic water feeder operation (pressure too
high), or defective valve (leaky). True, you only have to report the
valve. Did you miss problems at the other components?) Corroded relief
valves also need test and repair/replacement
Do not touch the relief valve- it may open and fail to shut
Do not pick at corrosion as you may start a catastrophic, un-stoppable leak requiring total system shut-down.
Different water pressure/flow observed in the kitchen:
hot water pressure significantly less than cold--is a tankless
coil installed? is a water softener installed? is there "hard"
water--have mineral deposits clogged the coil? Are there "cleanout"
plumbing fittings on the coil piping? Does this suggest a history
of clogging and acid-flush treatments? Can a clogged coil be repaired
or replaced? How severe was that rust you observed at the coil mounting
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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, Dan Holohan, 516-579-3046 FAX
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).
"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.)
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
Links to our list of additional information on heating system inspection, repair, maintenance