Gas and Oil Home Heating Furnaces - Exhaust Fan Problem

I have a forced air gas heater-A/C with an electric ignition system. I replaced the control board for it earlier this summer when it shorted out and the A/C worked fine.

The problem I am having now is that the heater will only turn on once. When I shut it down and turn it on (following directions on furnace) the electric element sparks the flame and the furnace runs fine, heating the entire house easily. Once it reaches the temperature on the thermostat, the burners and blower turn off, and the exhaust fan stays on. The exhaust fan will stay on indefinitely at this point, and the furnace (as far as I can tell) will never relight.

Hello Kelly Logan. Welcome to our Heating and Cooling forum and the Do-It-Yourself Web Site.

The exhaust fan relay may have become damaged by the shorted out circuit board or whatever cause the short to happen. The fan relay should be located inside the control box where the circuit board in located.

Some units have the control panel in the blower compartment while others in any other location available. Varies from manufacturer & model. Your brand and model info not posted.

If you need to see the part first to identify it, the local parts store or dealer will have the part, if it's not already on that circuit board recently installed.

Several other resident heating professionals replying within this forum, could have additional helpful information, suggestions, advice. Check back on your question several times for additional replies.

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TCB4U2B2B Company Enterprises. Energy Conservation Consultants & Gas Appliance Diagnostics Technicians.

what is the make/model?

It's a Goodman GMP Series: Multi-Position Induced Draft Gas Furnace GMP075-3.

I saw another entry that described a similar situation and suggested cleaning the flame sensor, which I have to no avail.

I'll check on the relay. I only see one on the part list so far. :^)

I have checked the air pressure switch, and it appears to be working (the diaphragm opens and closes the switch).

Another oddity is that the exhaust fan comes on even if the thermistat is set to Off.

Maybe you got the wrong board it is hooked up incorrectly ??

It looks like the board had sustained water damage that took out the exhaust (draft inducer?) fan relay. $200 and a new board later, all better.

Thanks all, for your information.