Nest thermostat continually heats

[JoeR1939]

My Nest battery was low and thermostat was offline. I hooked up a recommended 24v supply and now it heats constantly.  My old honeywell wiring is blue & blue/white twisted together to W1 and orange & orange white twisted together to Wh.  24v hookup went to C and Wc as per instructions. Any help is appreciated.

[Markjosephp]

Hello  JoeR1939, 

Thank you for taking the time to let us know about your inquiry. I'd love to know more about this.

Could you share with us photos of your old and current thermostat's wiring? Could you provide a rundown of all the steps you've tried? Also, please check your actual thermostat's power readings in the Technical Info settings for the Nest Learning Thermostat and the Nest Thermostat E or the Equipment settings for the Nest Thermostat 2020 model.

I'll look forward to your response.

Regards,
Mark

[JohnS13]

Nest thermostat is on USB cable, display is normal, no errors, but continuous heating. It has occurred three times in the last couple of months. Display shows temp set to 18, current temp 22, but the boiler and radiators are active. Quick fix is to just power off but that doesn't help diagnosis 

[Markjosephp]

Hi there,

Oh! Thanks for the details. Does your thermostat have a C wire? Can you help me check its power readings from the Technical Info? This will help us determine if this is a power-related issue.

Regards,

Mark

[JohnS13]

If I understand the question, power is from a Micro USB cable not USB-C. I don't know anything about power readings, what does that involve?

Thanks 

[Markjosephp]

Hi there,

I'm sorry for the confusion. To be clear, what type of Nest Thermostat do you have? Also, from what country are you posting?

Regards,

Mark

[JohnS13]

Please see screenshot / link

Nest thermostat 

[Markjosephp]

Hello there,

I appreciate your effort. I don't have access to the link, but I did send a request for viewing. Please keep me posted once it is granted so I can check it here on my end.

Regards,

Mark

[TudorL]

Hi there @JoeR1939, 

Let's perform a quick click test. If you have the thermostat on the Nest app, I'd like you to go with the app near the Heat Link and call once for heat and let me know if you hear any clicks. Wait for one or two minutes and then stop calling for heat and let me know if you hear another click. 

[JohnS13]

Yes, clicks heard as you describe.

[TudorL]

Thanks for all the info you've provided. Please let me know if I can send you an email on the address you have associated with the Google Community account, as we'll need to go through a few extra troubleshooting steps. 

[JohnS13]

Yes, happy to receive any suggestions about troubleshooting, especially if/when the Nest thermostat plays up again. Thanks 

[TudorL]

Great, you'll receive the email from me in the next couple of minutes. 

[OannaCG]

Hi there! Could you please let me know if you received the email sent by my colleague? 

[JohnS13]

I sent an image response on 6 May via email (not this platform cos it doesn't include an image option). Let me know if this hasn't happened or if I need to respond differently. Thanks for following up

[OannaCG]

I sent you an email, please reply to it with the picture, because I couldn't find the email you sent previously and let me know here once it's done.

Thanks.

[JohnS13]

Hi Oanna, I only see postings here on this topic, I have not received other types of email - just the community mailer advising me of a new posting

[OannaCG]

Thanks for letting me know. I sent it once again. You should receive it. Please check your inbox and tell me if you received it.

[JohnS13]

Nothing in email or spam, not sure what's going wrong

[AlexD]

I located the email you sent to us on the 6th of May, that was in reply to my colleague requesting the picture. I replied to it with some further instructions. Check your Gmail account and let me know if you received it once you've gone through it. 

[JohnS13]

Hi Alex, I received a link to Verify my account, that's all so far

[AlexD]

That was me, no worries. I can see the image now. The wiring is about what is expected. It seems you have a system boiler with a Y plan valve.

Let us do a bit more testing similar to what you have done with my colleague regarding the click. 

This time go to the hot water control side and tap on the upper right corner cogwheel to go into the hot water settings. You will see a toggle there, the first one that is on/off. If it is on, set it to off while we test. This will disable the schedule, if any, and you can toggle it back on after. 

Boost the hot water and listen for a clicking noise, like for the heating side before. Stop the hot water boost and listen for a clicking noise again. Let me know what the results are.

Additionally, could you let me know how long has the thermostat been installed for and working as expected before you first noticed this behavior? Was it installed by a Nest Pro or by a heating/electrical engineer?  

[JohnS13]

Thanks Alex. Hot water was Off anyway. It clicks ok when turned on (boost) and also clicks when turned off. Installed May 2018 by heating engineer. First occurrence of continuous heating was maybe November 2022, when the thermostat was wall-mounted about 6 feet from the control box.  Now the thermostat is table top on a USB cable in the lounge (saving heating energy) about 15 ft away from the box, since maybe February this year.  All worked well until just before I started this support request. Thermostat generally well behaved but it's like a Software panic sets in between the thermostat and the box. Not very good diagnosis I'm sure but I've seen enough stack overloads to be suspicious. My only remedy has been power off, wait a couple of minutes, then resume power

[AlexD]

Thanks for checking and the information. While the hot water was not a problem it is still good to do the same test as the heating side just to check. 

Since you hear a click each time, that would indicate the Heat Link is working as expected. The command from the Nest app is sent to the thermostat display, the display passes it on to the Heat Link and the Heat Link moves the internal relays with an audible click noise. 

Since based on the picture you have a Y plan system it is most likely that what's going on is the valve getting stuck. I would recommend you have the Y valve checked if you haven't already. 

There is some deeper troubleshooting we can do on the Heat Link unit, but this will need a multimeter that can check continuity. If you wish to perform the test on the Heat Link, if you are comfortable in doing so or can have an installer carry out the test I can email you the steps for the continuity test. Although, based on the click test, the thermostat and Heat Link seem to be working as expected. 

[JohnS13]

I will get the Y valve checked. For now I believe the electrical continuity is fine but I'd be happy to double check with a multimeter. Please provide that info, as ever your help is appreciated 

[LarisaL]

Hi there @JohnS13! I just sent you the steps for the continuity test via email and you can reply with the diagnostic report to it. Please let me know once you've done it. 

Many thanks, Larisa.

[Paul_R]

Hello @JohnS13! It's okay if you do the test with a multimeter if you are comfortable to do so, just make sure to take safety precautions. Also, please follow the instructions my colleague has provided via email regarding to the diagnostic report. We'll wait for your update once you are able to perform the test. Have a great day until then

[UanaC]

Hello there! Just checking in with you. Did you see my colleague's previous message? 

[JohnS13]

Hello, yes but it will take a long time to get my plumber to check, he's very busy on bigger jobs. I can check all connections myself with a multimeter etc. but not for a few days. Thanks for checking back, I will submit a response but not from a highly expensive installation specialist

[UanaC]

Hello there! Just checking in with you. Any updates regarding the test?

Thanks in advance , Oana.

[AlexD]

Hey there, I haven't heard from you in a while so I'll be locking this thread. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community. Thanks, AlexD.