Heat won't shut off even after reaching temperature set point

[newcire]

My learning themostat often keeps the heat on despite reaching the desired temperature. Its resulted in a few sweaty, late night wake ups. The only way to seem to stop is turning on and off the furnace breaker.

It doesn't always do this but its very annoying when it does. It tends to occur more often late at night.

I've checked and rechekd the wiring. Any ideas?

[AxelD]

Hi newcire,

Thanks for posting and sorry to hear that your thermostat keeps running the heating. No worries, help's here! I have a few questions I'd like to ask about your system:

1. Could you provide a photo of your wiring?
2. Do you have a C-WIRE connected?
3. When did you install your thermostat?
4. When did the issue start?

I'll wait for your responses, but, in advance here you have some steps to Troubleshoot strange heating or cooling behavior. 

Let's try it and let me know how it goes.

Regards,

Axel. 

[CATinDenver]

Axel, I'm having almost the exact same issue, except that my Nest spontaneously turns on the furnace when it ISN'T set to come on at all.  Even when in COOL mode it randomly comes on and it won't shut off.  There's no way to turn it off no matter what I do with the thermostat. I have to turn off the furnace breaker to make it stop.  The thermostat currently is NOT set to Eco, and has no schedule set.  We are using it completely in manual mode.  We had Nest installed in March with a professional HVAC company along with a new Lennox furnace and A/C unit (not a heat pump, no boiler, it's a 2-stage gas furnace).  The runaway furnace thing happened twice in the first month so they came and replaced the Nest thermostat with a brand new one.  Now it has happened twice more since May. They assure me that the C-wire is connected.  One more interesting point:  We have two furnaces, one upstairs, one downstairs.  The downstairs Nest has had no problems whatsoever.  It's only the upstairs unit that this keeps happening.  Would love your insight!

[AxelD]

Hi @CATinDenver,

Thanks for posting in the community! Sorry to hear that your system keeps running the Heating even when you don't request it. No worries, help is here! I'd like to ask you some questions to gather more information:

1. What type of Nest thermostat do you have?
2. Are there any error messages? If so, what are they exactly?
3. Do you notice any intervals or specific patterns between these strange behaviors?
4. Have you checked the article to Troubleshoot strange heating or cooling behavior?

Keep me posted.

Regards,

Axel. 

[CATinDenver]

Thanks for the response Axel.  Here are answers to your questions:

1.  It's a Nest Learning Thermostat, purchased in April, 2024, but I don't have it set to the "Learning" setting. And it's not set to Eco.  

2. No error messages.  In fact the thermostat doesn't even seem to register that the furnace is on. In a normal situation when the furnace is on, the dial turns orange.  When this unexplained furnace episode happens there is no orange on the dial.

3. Zero patterns or situations.  It's totally random at different times of the day.  I have not set any schedule for this  thermostat,  This week was the most unusual of these episodes because the thermostat was set to COOL, yet still at 6am the furnace came blasting on. 

4. Yes I've read that troubleshooting article a few times. My HVAC contractor assures me that there is a C-wire and it is connected.  He has been here 4 times now, checked and re-checked all the wiring, the furnace, reprogrammed everything from scratch, done everything he can think of, to no avail.

5.  In my reasearch of other customers postings I am learning that I'm not the only one with this exact issue with Nest thermostat.  So I'm wondering if Nest has figured out how to fix this problem?  Thanks for your help!

[AxelD]

Hi CATinDenver,

Thanks for your reply! I appreciate all your responses, they are very helpful to understand the situation. Based on all the troubleshooting done by your contractor, that is the recommended one. Please fill out this form and an agent will contact your as soon as possible with further troubleshooting.

Regards,

Axel. 

[Mcmillenta12]

No common wire connected.

Just r and w on boiler system. 

Boiler continuously runs and has call for heat even when thermostat is off

[AxelD]

Hi Mcmillenta12,

Thanks for replying. Sorry to hear about your system running even when it's off. No worries, help is here! In this case, it's always recommended to install a C-WIRE. This will provide enough power for your thermostat to function properly. Let's take a look at the next article to Troubleshoot strange heating or cooling behavior, it contains some steps that might help to fix this.

Regards,

Axel.