Nest 3rd Gen Thermostat issues with ambient temperature readings and boiler short cycling

[Robjack56]

I'm on my 3rd set of Nest thermostats in 2 months. 2 zones, upstairs and downstairs, 1 nest for each zone, oil heat/radiators with Peerless boiler 12 years old. I had manual Honeywell round thermostats. One died so decided to upgrade to Nests. My wiring setup is 2 wires, 1 red and one white. Online check and then phone call with Nest reps confirmed my system was compatible without needing a C wire. Ambient room temperature is 6-8 degrees less than readout on Nest thermostats. Boiler is short cycling. Very helpful google people have spent many hours troubleshooting over chats & phone. 

Going through the Pro setup shows power connection is green but heat connection is yellow, denoting need to check. Google reps couldn't answer why that is. HVAC tech just came for annual service, boiler in excellent shape, he said it may need a C wire. 

Before I spend money on 2 C wire adaptors and a couple hundred to have them installed has anyone experienced this issue? I might just go back to the manual Honeywells, simple & reliable.

Thanks 

[Patrick_Caezza]

Not sure who told you that a two-wire heat-only system is compatible with the Google Nest Thermostat without a C wire, but it is not.

A C wire is required, and you can run a new cable with three wires or use the Google Nest Power Connector.

An external 24Vac transformer might also be required if there is no C terminal at the boiler and zone valves.

Does your system have a valve zone controller or just two individual valves?

[Robjack56]

Hi Patrick,

Many thanks for your email. 

Both the online compatibility checker and a Google Nest rep confirmed it would work. Cest la vie. 

I have a 2 zone setup with separate controllers (I believe) and a 24 V transformer on the top of the boiler. I will p/up the Google Nest power connectors.  I was just about to give up after all the hrs spent sussing this out. 

[Markjosephp]

Hello folks,

I wanted to ensure that everything was covered here.

Thanks for the help here, @Patrick_Caezza.

@Robjack56, I'm sorry for the trouble this may have caused you. Here are some references to help you install your new Nest Power Connector on your HVAC system.

• Nest Power Connector installation article
• How to install the Nest Power Connector - video link

Please let us know how the installation goes.

Best,

Mark

[Jake]

Hey there,

I wanted to check in and see if you are still in need of any help. Please let me know, as I would be happy to assist, and answer any questions you may have.

Best regards,
Jake

[Jake]

Hey Robjack56,

I wanted to check in, and let you know that I will be locking the thread in 24 hours.

Best regards,
Jake