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I have a Lennox G21 pulse and it needs to have power removed…

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I have a Lennox G21...
I have a Lennox G21 pulse and it needs to have power removed and put back on to make it start. It has been fine until we started getting zero degree nights. Now that it is back in the twenties it works fine, any suggestions?
Submitted: 7 months ago.Category: HVAC
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Answered in 25 minutes by:
12/18/2017
HVAC Technician: airheatman, HVAC Technician replied 7 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,182
Experience: Furnace, A/C and heat pump specialist.
Verified

Troubleshooting the G21 is going to be a step by step process which we need to do when it should be on and is not. I can upload the service manual showing these steps if you would like and we can go through diagnostics together when it fails if you would like.

The two main reasons for it not to come on is an open limit or an open differential switch.

As for it only happening on colder days, I am inclined to think it could be a limit opening on days the furnace has to run longer to keep thermostat satisfied.

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HVAC Technician: airheatman, HVAC Technician replied 7 months ago

Let me know if it the G21R or G21Q

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Customer reply replied 7 months ago
Without looking at it I'm not sure at work right now. All I know is it is variable speed 1 horse motor with an ECM
Customer reply replied 7 months ago
No live call I will get more info thx
HVAC Technician: airheatman, HVAC Technician replied 7 months ago

Get me complete model when you are there and we can go from here.

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