Boiler activates every time Nest Learning Thermostat's screen is on

[alex-l]

Just installed Nest last night and was trying to figure out why it makes the boiler run non-stop, even when heat is disabled/temp is set very low. Spent a few hours on chat with tech support, but they were not able to solve the issue and promised to get back to me.

I just figured it out after a long day of observations. Every time I pass by Nest and the screen is activated, it sends a signal to the boiler to warm up. Same, all the time I'm configuring something and Nest's screen is on, the boiler keeps running. Once the screen goes dark again, the boiler shuts down almost immediately. 

Now the question is, how do I fix that? The whole cycle of heat and post-pump takes time and definitely going to cost a lot of money since the thermostat is installed in a hallway and going to be activated all the time!

[Patrick_Caezza]

Where are you located, UK/Europe or USA/Canada?

[alex-l]

I'm located in USA

[Patrick_Caezza]

How do you have the Nest wired?

[alex-l]

Only W1 and Rh wires, same as my old thermostat (I have this boiler for radiant heating). Note that everything works as expected except that when Nest's screen is on (via Farsight or when I manually click the ring), it starts calling for heat without a reason

UPDATE: just noticed that the boiler is waking up for just a few seconds even when I don't touch Nest (Farsight is disabled for now). Looks like it happens when Nest is checking weather in background or something like this.

[Patrick_Caezza]

This is a common problem on many two-wire heat-only systems like you have.

You need to add an external 24Vac transformer so you get a C wire.

This is the easiest way to do it.

 

 

[alex-l]

Thank you. Although do I need both plug-in transformer and Nest Power Adapter? Can't I just use a transformer to plug it in Nest directly? Reviews on Amazon suggest that it works if connected like this

[EdwardT]

Hi alex-l,

Thanks for the response. That's another option to get a common wire for your Nest Thermostat, though I would suggest getting a technician to install that transformer.

 In most cases, Google Nest thermostats can charge their built-in battery using the customer’s heating and cooling wires. But there are situations where they may need to connect the Nest Power Connector or a common or C wire to consistently deliver power to their thermostat.

Thanks,

Edward

[EdwardT]

Hi alex-l,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

Thanks,

Edward

[EdwardT]

Hi alex-l,

Just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward

[alex-l · Accepted solution]

Yes, thank you. Regular plug-in transformer worked out for me.

[MelbaDT]

Hey there, 

Thanks for getting back to us and I'm glad to hear that you've got a working thermostat now. 

Cheers, 

Melba

[MelbaDT]

Hi, 

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the community.

Best, 

Melba

[EdwardT]

Hi folks,

@Patrick, thanks for the help!

@alex-l, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[alex-l]

Yes please see my reply above. Looks like Nest advertises that it can be used without C wire, while in fact it's not true.