I have a furnace about 22 years old and I just replaced the circuit board and thermostat and when I lit the pilot all seemed ok. When I turned up the thermostat the blower kicked on for just a second or two and then kicked off. Anybody have an idea about why this is happening?
Flame sensor is faulty? ie it shuts down when it fails to detect a flame is present. There are several technologies. Depends on which one you have.
It may simply need removing and cleaning.
Could be a photocell or a thing like a spark plug with along wire goes into the flame. --(electrode measures resistance. Flame resistance is very low. No flame is very high) Latter is more likely.
We need more information as to what kind of furnace this actually is. We don't even know the fuel. What we have so far does not sound right for an oil or gas furnace. When the thermostat calls for heat, the blower does not normally start right away. First the furnace fires and when the plenum temp gets hot enough, then the blower kicks on to start moving the air. That avoids cold start up blasts of air. That normally takes 30 secs to a minute, so I don;t understand how the blower could be shutting off 2 secs after the thermostat calls for heat.
Newer furnaces have an inducer blower for the combustion air. If it were a newer furnace, I would think that might be what is being referred to as the blower. But this is a 22 year old furnace and I don't think they were around back then?
Well there's your problem.
The furnace isin't old enough if it has a circuit board.
I should have mentioned it is a natural gas fired furnace.
That's a start. But what about the rest of what I asked, which is to say what blower comes on when the thermostat calls for heat and then shuts off in
2 secs? The air handler blower on a gas furnace normally comes on 30 to 90 secs or so AFTER the furnace has fired. Does the furnace fire up and light for the 2 secs? You need to describe exactly what is happening.
Actually, I have a 25 year old furnace and it has a blower for the exhaust gasses using 2 inch plastic pipe to exhaust the fumes to outside.
Ok so it does not fire up either. It is the only blower on this unit as far as I know
On 11/12/2011 12:32 PM, snipped-for-privacy@juno.com wrote: ...
Suggest giving actual model/manufacturer for reference, as well.
One basic question--did you remember to turn gas "On" after lighting the pilot?
But, if the circ fan tries to run immediately on heat demand, you've got either something wrong on the board replacement or the thermostat connection wrong or you have no preheat setting in the new controller.
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It sounds like you wired it up wrong.
Good guess. I went over everything and found a loose wire in the thermostat and I also replaced the Thermocouple and now it all works like new. Thanks.
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