E74 shown on the 3rd nest learning when other thermostat started the boiler

[lcmy]

We tried 3rd nest learning thermostat to control the temperature in bedroom at 2nd floor. There are two old round honeywell thermostat for the 1st floor and basement.

The nest learning works well on its own to start and turn off the boiler. However, everytime when the boiler was started by other thermostat, it showed 'E74' code. Once the boiler was turned off, the nest learning thermostat went back with normal display. It did not show 'E74' when the boiler was turned on due to lower temperature than the setting on google nest.

As the nest learning showed error, the boiler would heat both the 2nd and 1st floor, which cause low battery issue after long time use of nest thermostat. 

Does anyone know how to solve this problem? Thanks.

[aatienza]

Hey lcmy,

I’m sorry to hear you’re having trouble with this. No worries, we'll check this out. What type of HVAC system do you have? When did it start happening? Could you check if the breaker is turned on? What is the power reading of your Nest Thermostat? You can find this information by going to Settings > Technical Info > Power.

Looking forward to your response.
 

Thanks,

Archie

[aatienza]

Hey there,

I just wanted to follow up to see if you still need our help. Please let us know as we would be happy to answer any questions you may have. 
 

Thanks,

Archie

[aatienza]

Hello there,

Just checking in to make sure that you've seen our responses. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.
 

Thanks,

Archie

[lcmy]

Thank you for your questions and follow-up emails.

type of HVAC system: R, W, Y system.

I do not know how to check whether the breaker is ON or OFF. The nest works well if other thermostat does not start. The power is over 3.7 or 3.8V.

[EdwardT]

Hi lcmy,

Thanks for the response. We'd like to know more about this. Please fill out this form so we could investigate further.

Thanks,

Edward

[lcmy]

Thank you, Edward! It works fine now after we disconnected other thermostat.

[Juni]

Hello there,

I’m glad your issue is resolved now. I’ll keep this thread open for 1 more day. If you need further help, let me know.
 

Regards,

Juni