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Furnace not restarting after power failure

QualityGuy
Community Member

Troubleshooting my Lennox furnace (G61MVP-60C-091 High Efficiency Natural Gas) not restarting after a power failure - the Nest Learning Thermostat indicates it's calling for heat but the furnace will not restart after a power outage.  I have to turn the power off and then back on at the furnace (switch receptacle at the furnace) and then it will restart, but will not recover automatically as expected.  Not sure if it's thermostat (calling for heat before the furnace mail circuit board has a chance to reboot) or something else causing this issue (main circuit board of the furnace, power switch receptacle at the furnace, circuit breaker at the main power panel).  Any ideas where to start troubleshooting?

12 REPLIES 12

MelbaDT
Community Specialist
Community Specialist

Hey QualityGuy, 

 

Thanks for reaching out and sorry for the delayed response. 

 

In order to fully isolate if the cause of your thermostat not restarting is the Nest thermostat or your HVAC system itself, do you have another Nest thermostat or perhaps the old thermostat that you've replaced? If you do, could you try connecting it to your furnace then try to call for heating? Let me know how it goes. 

 

Best, 

Melba

QualityGuy
Community Member

Single nest thermostat (gen 3) - using Y1 (COOL -blue), G (FAN -green), W1 (HEAT -white), Rh (POWER - red).  After power outage - thermostat calls for heat but furnace never fires.  I have to powercycle the furnace and then everything is ok.  either timing related to the furnace control board booting to the nest call for heat - or something else, just cant figure it out.  Im concerned that on a cold day after a power outage if the furnace does not comeback on that the pipes might freeze if we're not home to powercycle the furnace.

rothertron
Community Member

Hello - I am having the exact same issue.  In my case the Nest will continue to run the outdoor A/C compressor non-stop while the furnace isn't running and it causes water damage and a lot of frost build up if I don't catch it right away.  (I also have a G1MP)

my HVAC guy said that a lot of Nest thermostats act funky unless you actually have the common wire attached - Google/Nest seems to differ with that - so we rewired the Nest to have the common wire attached and it did NOTHING to correct the problem.  I've got to check the rev on my control board because I read that the latest version (03) takes care of this issue but I haven't verified it.  I hate spending money on a new control board when this is a known issue with Lennox G61 furnaces but they won't admit it.

I thought the same thing, but I also don't know if the old thermostat had the same issue, but it was much more traditional with just the AA batteries in it.  I have the Blue C wire as I think it's key for the NEST to stay topped off on power and it functions better that way.  But even with that wire this issue happens.  It's during a momentary flicker of power, longer outages and it sometimes starts up ok.  I am leaning towards the actually issue being the Lennox PCB early revisions.  I have found info online indicating other people had issues, but not the same as mine. Because the NEST is giving the demand signal for cooling and the wires are on the same post it will turn on the A/C outside even if the furnace is non-responsive.  The furnace will reset, but only if I turn if off for say 5 seconds and then back on again.  People have has success with the new rev of the PCB so I purchased one on AMZN for US$111 to try.  If that doesn't work my plan is to actually see if I can integrate a UPS style device to the PCB power supply so that it never shuts off during a momentary outage.  Sorry to hear you are dealing with my same woes, I think my furnace is from March 2009 so it's well out of the warranty period I think.

Did you have any luck with the newer version of the control board?  Im not even sure how to go about setting up a small UPS for the furnace and Im hesitant to buy a new controller from Ebay because who know if it will work or not.

The new board has been installed since August 30th.  I have not had any issues.  In the process I disconnected the whole home humidifier to reduce complexity of problem solving.  One thing of note that seems to be something new is that the Nest will now show "POWER OFF" as a status on the APP when I trip the furnace and it fires back up again.  Prior to this I never noted that the Nest could tell the power was off.  Unfortunately I am now at the tail end of the A/C running for summer, but I will see if I can force the A/C to run by lowering the temp and killing the furnace power and seeing if it shuts off the compressor outside.  Will let you know.

KGB
Community Member

I am having the same issue with the same furnace. Did you manage to get it solved?

rothertron
Community Member

Yes, I believe the updated to the control board has fixed the issue.

QualityGuy
Community Member

So after a lot of research i seems that Lennox had problems with the control board (100870-01) which is marked hear the thermostat wire connectors.  Supposedly the newer versions of the board (100870-03) fixes this power failure startup condition.  My furnace is 13 years old and also has a issue with the Honeywell 2 stage gas valve and it's too costly for me to dump money into this Lennox G61 to replace the valve and the board - so I'm replacing it with a American Standard S9X2 (same as Trane) to get a new 10 year warranty with higher efficiency (along with local energy company rebates and fed tax credits for Energy Star Certification).  Lennox would never admit there was an issue with the control board to my knowledge and I could never get it replaced under warranty while my system was covered so I'm done with Lennox products all together.

added my notes here below, good luck, seems to have done the trick

rothertron
Community Member

Sharing these with everyone.  I just did a quick test of two power outages, a quick blip and a 2-second outage.  In both cases the furnace recovered properly and the A/C did not run unless the furnace was running.  It also appears confirmed the Nest is seeing the power is out and applies the proper delay to keep the compressor safe outside for the A/C (the nest never showed these things before if the furnace was not booted up, it would just keep running the A/C).  Cross my fingers I don't have to deal with any issues with ice on my lines again getting my basement wet and possible damage to my compressor/condenser.Screenshot_20221003-140342.pngScreenshot_20221003-140402.png