[SOLVED] do I have a bad thermostat? oil burner

[wAYNE]

This AM, noticed that the oil furnace blower continued to run despite burner stopping to the point where it was blowing out cold air continuously. Upon manually disconnecting furnace from AC and then reconnecting, blower immediately restarted.

When I disconnect the thermostat from the control module, with AC applied to the furnace, the blower now doesn't start. Checking thermostat for continuity throughout its range with ohmmeter, I find 0 ohms no matter the thermostat setting. From this, I deduce that the thermostat is malfunctioning and needs replaced. Is this correct?

Thanks in advance.

[wAYNE]

Ok, so removing the thermostat cover and moving the adjustment back and forth a few times, it now seems to be working again. A lot of dust in there. I'm going to see if I can blow out the area with compressed air. Any other cleaning ideas welcome. Thanks.

[micky]

Not too surprising

Definitely not surprising.

Not enough info, but I don't care.

No. If it turned off the burner at the right temp, the thermostat works and the problem is, I think, in the switch that turns off the fan. The fan is designed to blow for a while because the burner is still hot enough to heat the house for a while after the fire goes out. Not blowing would waste that heat, and maybe, I don't know, on occasion overheat things near the firebox.

The switch is the same one that delays turning the fan on until the burner has run for a while. On mine, I think it's in the upper right corner when you take off the access door. I think part of it sticks into the furnace.

I haven't heard of one of these breaking but I'm not in on the gossip connection.

What make of furnace? If it's a carrier, I can tell you wire colors.

The furnace probably came with a wiring diagram, or you can find one online, and you can see which colors of wire switch open when it's cooled down, and you can use a meter to see if they are really open. Probably not.

[micky]

Sample images, discussion. I'm not suggesting you replace it without confirming that it is the problem.

Also, any chance you changed the fan switch on thermostat from Auto to On? Check that first. I should have said that first.

[wAYNE]

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The problem was that I ran out of oil! Once refilled, I primed and bled and all ok now. Thanks for the suggestions though.

[micky]

Thanks for getting back to us. Not everyone does, including me (although in my case it's always because I'm waiting for more info. maybe theirs too).

I've run out of oil and my fan didn't keep running. But we have different furnaces. Maybe for yours it's meant to be a signal that you've run out of oil!

[wAYNE]

You're welcome. Although I've seriously reduced the thermostatic temperature over the last two years to help offset skyrocketing oil costs, the furnace still does run occasionally.

No, I think a separate issue had developed with the thermostat causing the fan to keep running. After I removed the thermostat cover, I noticed that the dust present within was causing the switch to stick in place instead of moving like it normally would have when I adjusted the dial up or down. Since thoroughly blowing out with compressed air, no more sticking and operating normally.

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