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Carrier Furnace Operations


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I have a technical question regarding implementation of my Carrier furnace within my residence. Specifically, the furnance has been installed for 17 years and I have not had any problems with it. I have noticed that occassionally (less than once a year) the pilot light will extinguish preventing ignition of the main burners during a call for heat. However, I have noticed that during a call to heat where the pilot is not lit, the inducer motor starts followed by the blower without the burners lighting (presumably due to the lack of the gas valve being opened with no pilot). When the pilot is not lit, continuous inducer/blower occurs. Is this the desired mode of operation of the furnace. If the pilot should go out when no one is in the residence for an extended period of time, the inducer/blower will continue to run as the residence will not be heated. Please advise. Thank you.

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It's been my experience that it will run until the furnace tries a couple of times to light itself, and then re-boots itself, before the micro-processor shuts everthing down. How long did you wait after cutting off the pilot to see whether it would run on 24/7?



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The short answer is that you need a thermocouple and to a lesser degree recalibration or new board.

Here is the long answer

The sequencing is controlled by a computer that starts out with a call for heat. I'm assuming your thermostat fan switch is set on AUTO and is not affecting the operation of the blower.

The inducer fan turns on to proof the vent or make the pressure switch happy. That ensures the vent is unobstructed and clear for service.

A signal is sent to authorize ignition but if the pilot light is off the gas valve will not open and the sequence should be terminated.

On a hot surface igniter system the valve opens BUT if the flame rectification on the opposite side of the ignition point doesn't sense heat it will shut down the gas valve. The system will attempt ignition three times then shut down. To reset it, turn the appliance switch off then on again. Your standing pilot system may not have this sophistication built in or the puter is confused .....who knows.

Quote "(presumably due to the lack of the gas valve being opened with no pilot)"

On a pilot system the gas valve will not open unless the thermocouple is happy and has no effect on the blower.

The blower is activated by heat limit sensors which have nothing to do with the proofing process. Having said all that, I've observed both fan and blower come on at the same time and I'm thinking someone tinkered with the programming at some point in the developmental stage, or the program is faulty or corrupted.

Regardless, you have a no heat potential and the system should be serviced. I would replace the thermocouple ASAP. I would defer replacing the board, it will cost you more than the value of the appliance .

Hope this answers your question.

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