Heat pump stops running below - 8C

[PylonSquelch]

Hello, 

I have a dual fuel system with a heat pump and a forced air gas furnace. Nest has been working great for the past few years with gas furnace. This is the first winter the heat pump has been in use. When the temperature drops below - 8C the heat pump stops heating, the heat pump fan doesn't run, the furnace fan continues to run but blows cold air and the indoor temperature drops. This tends to happen late afternoon after the thermostat switches from 17C to 18.5C, after that I usually change over to alternate heat and switch back later.

The installer doesn't seem interested in resolving this issue and blames it on the thermostat. Given that this is a new system I tend to believe them but very disappointed that they are not into trying to fix this since they were aware before they took the job that I had a nest unit. They did look at the heat pump once when it wasn't exhibiting the issues as it was not a cold day and were able to go though a defrost cycle and begin heating, the technician had said he'd like to see it when it's not working but after multiple requests they have not taken a second look. 

I tried turning off various settings with no results and I've reset nest to factory settings.

Heat pump model: ICP TSH6 -International model- and is equivalent to Tempstar TSH6. 

Any suggestions on how to fix this would be appreciated.

 

@Jake @laurentbourg @AnaM @CristianC @Ashepherdson @Faris 

[PylonSquelch]

Looks like a wiring problem. Found answer on a A1 HVAC video below. Techs put alt heating wire in W2 alt. changed it to W1 and followed video for duel fuel setup. Currently testing. 

https://youtu.be/aAluyOpVzu0

[PylonSquelch]

Nope, after the morning heating, the unit went back to the same behaviour. Problem not solved.

After reading some other forum posts it would seem this is a update issue. Would be nice if my system were magically rolled back to an older version as someone suggested happened to them. 

Also, I set the system up with single fuel, running heat pump only. I removed the white W1 wire and reset the nest to factory. Ran fine in the morning but after the scheduled temperature increase late in the afternoon there was cold air from the vents and heat pump fan was not running. 

[Ashepherdson]

This is well above my head, but I'm escalating this so more advanced people can take a look.  I'll try doing some research on my end as well. 

[MellyMel63]

Happened to us yesterday to downstairs Nest. Coldest day of the year, ice storm here in the southeast. Thought Heat went out because of power surge. Nest thermostat upstairs still working fine. 12 hours later, heater came back on. This is not the first time this has happened.  Talked to Nest for 1.5 hours and never resolved. 
Nest faceplate showed “red” heater was on and trying to heated , but no air coming out of vents. Did all sorts of “resets”.  Alas, 1:30am, heater starts working again? What is happening? 

[PylonSquelch]

I hear you, it's frustrating and it appears to be because of the latest update. I've learned more than I've ever wanted to know about HVAC since this issue began. Don't blame my installer for not wanting to deal with this issue. 

[PylonSquelch · Accepted solution]

Since there doesn't seem to be any further advice from the community and a nest pro is too far away to service the unit, my solution to the problem was to remove the nest thermostat and install the old honeywell programmable. Works great now.

** Edit **

That resolution didn't last very long. After further investigation by the installer it was found that there were some faulty valves in the heat pump, they were replaced and its working fine with better performance. Will put nest back in place foll2a but of testing.