General questions about oil furnace

[Mikepier]

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?

Thanks

[Speedy Jim]

Hit the local library for a book on domestic oil burners.

Some info:

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 It may have been replaced by a newer design, using a flame sensing photocell.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.

[Mikepier]

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.

[Claude Hopper]

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.

[Mikepier]

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 correctly?

[Speedy Jim]

The speed of response depends on the thermal mass of the furnace. Thick steel plate could easily take 5 minutes to heat up.

[dpb]

Speedy Jim wrote: ...

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...

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[Tom Lachance]

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.