I've searched the archives for my problem with my Heil furnace but
couldn't find anything so here goes.
My furnace is a 1978 vintage system. It is an oil fed / forced air
system. I have been having a problem with it shutting down on its own.
I've narrowed the problem to it becoming air locked and starving for
fuel. All I have to do is open the pet cock drain, push the reset
button and let it run into a pan until clear oil flows and close the
pet cock and it then runs fine. This has been happening several times
beginning last winter and now has happened just recently.
Things I have done or checked:
a) Replace the oil filter
b) Check the breather pipe for blockage on the oil storage tank
c) Replace the nozzle
d) Replace the flame sensor
e) Tighten all fittings
f) The tank is over half full
Any other ideas or suggestions? The furnace seems to run fine
Thanks for the tip.
Didn't even know the pump had one? Do I need to take the pump apart to
get to it? Just wondering if the screen is plugged would the furnace
even run at all? Or does it sort of clear itself when I open the drain
pet cock? Thanks!
The pump screen is accessed under the pump end cover on most pumps,
should be like 4-8 screws holding the cover on I think.
Tightening the fittings may not always seal them and in some cases can
make leaks worse. Cutting back, re flaring and replacing fittings is
Do you have a single pipe fuel feed and if so is it gravity or suction?
It it's a gravity feed from the tank and stays low all the way to the
burner you usually don't get air in the line problems unless perhaps you
have such an accumulation of sludge in the tank that it's blocking the
outlet. If you take the filter off and put a pan under it do you get a
strong fuel flow if you open the valve?
If you have a suction setup (drawing from the top of the tank) that is
more likely to have airlock problems from the slightest leak at a
fitting. Also consider deteriorated gaskets at the pump of filter as
possible air inlet sources.
I see the 4 cap screws on the end of the pump housing. I assume
removing those should allow the cap to be removed and allow accessing
the screen. Right now after just having reprimed the thing since
yesterday, the furnace is doing ok but if it goes out again that will
be the first thing I will do.
I have a single pipe fuel feed which I think must be suction? But the
line comes out the BOTTOM of the tank and goes through the fuel filter
and is routed up through the upper floor joists over to the furnace and
then down to the pump. I have no leaks anywhere that I can see in
between. If there's a leak wouldn't it be noticed as a fuel drip if
the furnace is not running?
Also, if it goes out again I will remove the fuel tank filter and drain
some out and see if there is any sludge. I put a new filter on last
winter when I first started having the trouble and I thought I remember
doing that at that time.
I'll also check for bad gaskets.
Before you yank the pump cover off, order the screen and gasket kit
for that pump model. You won't be able to save the old gasket and
risk having no heat without a new one.
You're saying that the tank is one floor *below* the burner?
And it's a one-pipe system? Although that setup will work
under the best of conditions, it is very prone to failure
when there is the tiniest of vacuum leaks *anywhere* in the
suction line. That could be the packing on a stop valve,
the cover gasket on the filter, a flare fitting and on and on.
Go change the screen, but if you still have trouble either
investigate vacuum leaks or change over to a 2-pipe system.
It sounds like he said the line comes from the bottom of the tank, goes
up to ceiling level and then back down to floor level where the burner
As for the leak thing, it's quite possible to have a leak that lets air
in under suction conditions and does not leak any fuel outward when the
pump is inactive and the line is at a pretty neutral pressure.
Yes you have that right!
Then the leak would have to be up high somewhere? There are no joints
between the filter (down low) and the pump (down low).
I'll let you guys know what I find or do if it happens again. I am too
stubborn to call a repair man! Thanks!
The leak doesn't necessarily need to be up high. When the pump is
running and fuel is flowing, a bubble of air could be sucked in from a
leak anywhere along the line.
In a single line gravity feed setup where the line stays along the floor
all the way to the pump the line remains under pressure all the time and
there is little chance of sucking air in the line even if there is a
In a single line suction setup where the line goes up above tank level
(whether the line comes from the bottom or top of the tank makes no
difference) the reduced pressure allows air to be drawn in from any
leaks. These air bubbles will be very small, but they will be drawn
along and accumulate in the pump where they can eventually cause the air
With a two line suction system you can still draw in bits of air from
leaks, but when they get to the pump they don't accumulate to problem
levels because the excess fuel being pumped is returned to the tank via
a second line instead of being returned to the pump inlet as in a single
Other than the obvious advantage of finding any leaks in your feed line
before they become bigger, adding a return line from the pump to the
tank will most likely solve the air lock issues. Most pumps are designed
for this and adding the return line is generally as simple as removing a
plug on the pump and installing a fitting and the return line to the
Has something been replaced recently (like the burner)?
Are there two lines going to/from the fuel tank?
When we had our burner replaced (middle of winter on the coldest day), the
guy hooked it up, got it running , and said he would be back later in the
week to tidy up the install and be sure everything was right. Well, he
never showed up again and we didn't complain because the bill never showed
up either. The burner ran fine for that winter, but later we found out what
he needed to "tidy up". Seems that he never installed the checkvalve, or
got it backwards. We literally ran out of fuel early next season when the
tank was full. Took a different repair man no time at all to diagnose and
correct the problem, and the problem has not returned for over 10 years now.
I have no idea why the burner ran for as long as it did and why it failed
when it did as I'm sure the tank had more fuel in it when it failed than
when it was running that first season. I have no idea where this valve is
or what it does but it sounds like it might be your problem.
We just got home from a long Thanksgiving weekend and the furnace is
still working fine. The last things I did when it went dead about a
week ago was to re-prime the system and then after posting this topic,
I snugged up on all the joints and fittings on the line going to the
pump. Prior to doing this when the furnace was still working and just
before it went dead, when it started up it would sputter and shudder
almost like it was going to erupt. But now it seems to start up as
quiet and smooth as it ever has when it was working good. I'm
wondering if it was sucking a bit of air all along and when it would
start up it would be feeding an air/oil mixture and trying to ignite
that which caused all the sputtering? Finally when it got a high
enough air to oil mixture it would quit?
Thanks for all the great suggestions!
You may be fine, but as it was mentioned I think by Jim, replace the
screen on the fuel pump. If you haven't done this within the last two
years it will need to be replaced. I replace several on a yearly
basis's and the ones that I see are full of junk. It's probably in the
order of 5 or 6 bucks........Replace it! Don't forget the gasket and
if I remember correctly the screen should come with the gasket in the
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