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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Lennox 80mgf furnace, all runs normal. Ignition

Customer Question

Hi, my name is Neil. I have a Lennox 80mgf furnace, all runs normal. Ignition thru to house blower on, house blower shuts off after 30-60 seconds causing furnance to over heat and shut down.
Submitted: 1 year ago.
Category: HVAC
Customer: replied 1 year ago.
The house blower turns off prematurely, causing the furnace to overheat. This takes about 1 min with house blower running, then while the gas is still burning normal the house blower shuts off causing the plenum to overheat and shut down gas?
Expert:  Phil replied 1 year ago.


Your description sounds like it would be accurate. Pointing to a bad fan motor going off on its internal heat sensitive overload.... especially if the motor is over 10 years old.

If its a newer furnace it could be a bad printed circuit board.

Please attach a well focused, close up photo of the wiring diagram glued inside the service panel,you can use the paper clip icon at the right end of the toolbar at the top of this dialog box,Include a picture of the thermostat wire connections to the printed circuit board in the same area.

If there is no paper clip-icon, look for the '+attach files' link at left of your send button.

I can mark it up with trouble shooting instructions. You will need a multi meter ($30 at a hardware store) and some experience working with appliances, let me know a lot about your skill sets in those regards.

If none of this in your skill sets, tell me which direction you are from the center of the nearest city and I will look for a few well rated service outfits in your area.

Customer: replied 1 year ago.
I will take pictures when I get home from work. Will this session be available later, do I keep this window open on my laptop?
Expert:  Phil replied 1 year ago.

I am here almost all the time from 7 am 10 pm

You can also email yourself the link below. and use that to long in to this question.