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
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?
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
On 11/12/2011 12:32 PM, firstname.lastname@example.org wrote:
Suggest giving actual model/manufacturer for reference, as well.
One basic question--did you remember to turn gas "On" after lighting the
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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