I have a vacation home in upstate NY that has a Thatcher oil
furnace.Recently it had a problem with firing up. It turned out that
there was an air pocket in the line after a new oil line was run to
the tank. I was not sure how to bleed it. There was a flathead screw
on the motor assembly that I opened, and I did see a little air come
out, but it did not help. Then I opened one of 2 hex type bolts on the
top of the motor assembly, and that cleared the air pocket.
I'm trying to familiarize myself with how the system works, so here
are a few questions.
1) What are thses hex bolts for? Are they for bleeding or do they
control oil flow?
2) Do the burners need adjusting, and how are they adjusted?
3) There is a Honeywell stack switch at the base of the flue pipe has
been disconnected ( wires were cut) what was the purpose of this?
4) I have a Honeywell fan limit switch L498 that has an off-on-off,
that has a high limit of 200 deg which is suppose to shut the system
down if it gets too hot. Does this take place of the stack switch?
Hit the local library for a book on domestic
The stack switch provided the flame safety circuitry;
shut down in event of flame out/no ignition.
It may have been replaced by a newer design, using a
flame sensing photocell.
Fan limit does not replace the stack switch.
When I had the problem of no oil going through, it did shut down, and
I had to hit a reset button to start it again, so its possible a
photocell is now being used. Thats why I was concerned when I saw the
stack switch wires cut, I thought somebody took a shortcut.
What they usually do to bleed the line is remove one end of the copper
line that goes from the pump to the nozzle assembly, put a cup under it,
bypass the emergency shut off, and run it until the bubbles clear up.
What you did with the wrench could be anything depending on the burner
type. DO not adjust anything if you do not know what you are doing. You
probably invalidated your homeowners insurance policy.
As far as I could tell, that nut that I removed was tight on the pump
assembly. Once I loosened it I could remove it by hand. It did not
appear to be an adjustment. I did look at the flame and it was bright
white, so all looked ok.
While we are on this topic, how long typically does it take for the
fan turn on after you call for heat? I have the fan limit switch set
to come on at 140 deg. When I tested it, it took a good 5 minutes
before the fan kicked on. Meanwhile I was watching the dial on the
switch to see if it was moving. It was but very slowly. How can you
tell if the switch is defective or maybe not reading the temperature
And where the sensor is, of course, as well. 140F seems too high a
setpoint to me, also...
As an aside, I'd say it would probably pay to pay a service tech to come
look over the system and give you an owner's education on it...
The oil line is bled by a fitting on the oil pump that resembles an
automotive brake bleeder. Use a 7/16" wrench on the nut with a hose to a
container. Loosen the nut, start the burner, and when the line clears of
bubbles, tighnen the fitting and the burner should fire.
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