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Oil line clogging: cause & cure.
This article describes the causes and cures of blocked or clogged fuel oil piping or lines that are used to deliver heating oil to oil fired furnaces, boilers, or water heaters. We give emergency steps to keep heat working when the oil line is blocked and we describe alternatives to try before going on to replace an old clogged fuel oil pipe line.
We discuss using heating oil piping vacuum gauges, pressure gauges, and both hand pumps and CO2 blowout guns to diagnose, test, & repair clogged fuel oil piping lines.
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Symptoms of furnace, boiler, or water heater oil line clogging
These can include intermittent failures of the oil burner to ignite or to keep running, the system going "off on reset", a poor oil burner flame, and ultimately simply loss of heat when the burner will no longer start.
If your heating appliance includes an oil vacuum gauge on the oil piping (sometimes but not usually installed) you may see abnormally high oil line vacuum readings - the fuel unit is sucking away on the oil line but is having trouble pulling oil through the system.
Keep in mind that a high vacuum can also develop if the gauge is downstream from a blocked or dirty oil filter. Vacuums greater than minus-10 psi may indicate a blockage.
Westwood Products  and other suppliers distribute pump tester gauge sets (Reillo pump testers and vac-probe oil line access port testers) that can als be used to detect problems with the heating appliance fuel piping system such as blockages and leaks.
What causes a heating appliance fuel oil line to become blocked?
Fuel oil piping for oil fired furnaces,oil fired heating boilers, and oil fired water heaters can become blocked due to
How to Confirm that a Heating Oil Line is Blocked
Start by checking vacuum gauge readings on the oil line as we described above.
A hand pump or CO2 cartridge oil line blowout gun can be used to pressurize the oil line between its (for this purpose disconnected) end at the oil filter and its inlet at the oil tank.
How to De-Clog or Un-Block a Clogged Heating Oil Fuel Liine
Remedies for a clogged heating oil line depend in part on an assessment of just why the line has become blocked. IN the list above we give links to some oil line blockage problem causes and solutions.
First check the oil filter for clogging or blockage
Open the oil filter canister and take a look for thick goop inside the canister and on the outside of the oil filter cartridge itself.
Pull out (and dispose of) the oil filter itself. Now look in the bottom of the oil filter canister base for thick deposits of goop.
Clean that mess out. Also look for rust in the canister bottom - an indicator of excessive water in the oil storage tank.
Now replace the canister filter, reassemble the unit, bleed out the air from the unit, and check for functional oil flow. More details are
Try using a pressure and vacuum hand pump or a CO2 blowout gun with CO2 cartridge to blast open a clogged heating oil line
More generally, if the heating service tech thinks that the oil line is blocked by sludge or debris, before replacing the line s/he will often attempt to blast the debris and crud backwards from the connection at the oil burner all the way back into the oil tank. There are three approaches we've seen HVAC techs use:
Why might that approach work? Because it's common for some sludge to accumulate in the bottom of older oil tanks; the tank is installed (or should be) pitched slightly away from its bottom oil outlet port so that oil tank sludge or water that collects there (as long as it's not too much or too deep) will be kept away from the oil line.
Heating oil line cleanout or blasting is attempted using compressed air or more commonly a small portable canister whose end fittings accept a connection to the oil line flare fitting. The canister's other end accepts a CO2 cartridge. When the service tech screws the oil line blaster canister cartridge fully shut, a pin opens the CO2 cartridge, sending a blast of carbon dioxide backwards through the oil line.
If this quick and easy approach clears the oil line, you're back in business. (One may still need to bleed air from the oil piping lines after the fittings are reconnected).
Watch out: excessive pressures applied to the heating oil line can damage the piping, blow out the line, fittings, or other components, and can cause an oil spill in the building. Some oil line blowout gun models include a built-in safety valve to limit the outlet pressure to 150 psi to avoid this hazard.
Watch out: using a blowout gun or any high pressure method to try to clear a buried oil line is dangerous. The risk is that you create an underground oil leak - very costly to clean-up and repair. I'd use a hand pump or the (more popular) CO2 blowout gun that limits its output pressure to within the design range of the oil piping system, and I prefer to use only very low pressures to feel your way into clogs in buried oil lines.
Emergency steps to keep heat running with a clogged oil line
For buried oil tanks or other oil tank installations that use a dual oil line piping arrangement, one oil line is the supply (the one that has become clogged) and the second line is a return pipe that sends excess oil back to the oil storage tank.
Typically these installations insert the two oil lines through the top of the oil storage tank, and down into the tank to perhaps 6" from the tank bottom, and spread apart several feet (by bending the lines) so that the agitation of oil tank bottom sludge caused by the returning oil does not send sludge up through the oil pickup pipe.
If this is the arrangement at your oil tank and provided that the problem oil line is not totally blocked, we might keep heat running by temporarily switching the roles of the oil feed and oil return pipe.
That's because oil flowing backwards from the oil burner fuel unit (oil pump) to the oil tank has been filtered (before entering the oil pump) and will be less likely to have already clogged the return line.
Our dual heating oil line photo (above left) shows that just one oil line is in use at this oil fired heating furnace. Further investigation is needed to determine if the capped oil line is an old abandoned sludge-clogged oil pipe or if the system is limping along having been converted to a single oil line set-up.
Watch out: don't swap the oil supply and return line roles if one of these lines (probably the original supply line) is totally blocked.
Doing so can damage the oil pump at the oil burner, or worse, cause a dangerous leak of oil into the building if the higher pressure on the return line (caused by a blocked oil pipe) causes the oil pump (fuel unit) to blow a gasket.
Watch out: in a few oil tank installations at which a dual oil pipe system was installed on a oil tank that is located above ground, it may be possible to temporarily keep heat running by converting back to a single oil line system, using the "return line" now as the oil supply line.
But the oil pump unit on the oil burner will also have to be changed back to a single-oil line set-up. An internal bypass valve plug needs to be correctly installed for the fuel unit oil pump to work safely and correctly.
Replace clogged heating oil lines
If the heating oil line cannot be cleared with one to three blast-out tries using the CO2 cartridge, the heating service tech will most likely recommend replacing the oil piping.
We recommend using newer plastic-coated oil lines for better protection from corrosion and /or mechanical damage.
If the old oil line was just 3/8" ID or smaller, you might want to go to a 1/2" ID oil line to further protect against clogging in the future.
At "Question: how to get the heating oil line flowing after hurricane & flood damage" we describe using a CO-2 canister and cartridge to try to blast open a sludge or mud or debris-clogged fuel oil pipe or line following a building flood.
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Frequently Asked Questions (FAQs)
Question: Where to buy CO2 cartridges and gun for cleaning out #2 fuel oil lines from tank to burner
I need to buy CO2 cartridges and gun for cleaning out #2 fuel oil lines. Please tell me where I can get these in Manhattan or brooklyn. Wouild home depot carry this? Thanks, D.G.
The CO2 oil line blow out gun or "oil line blaster tool" that I have and use takes a CO2 cartridge that is a bit bigger than the ones commonly sold for use in seltzer makers and similar devices. I purchase refills at my local plumbing supplier who sells HVAC tools and equipment.
If you do not have a convenient local supplier for heating system test and repair tools, you can also contact the oil line plug repair tools distributors listed in the references section of this article, just below. 
Question: oil line clogging between tanks
[delete] (Feb 26, 2014) Anonymous said:
I ran out of oil. I have 2 large tanks that are connected. The lines were cleared, the filters changed, including the "crossover filter". I got oil delivered. The level indicates one tank is 3/4 full, the other side less than a 1/4 tank. Will the oil run smoothly or am I going to draw up sludge on the low tank? after I got oil why isn't it evenly distributed? Will running the furnace eventually even out the tank distribution?
Anon, it sounds as if the oil lines connecting the two tanks are clogged. Other possibilities include
- clogged or missing oil tank vent
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