NEST not running with heat mode.

[wg8569]

I have a Space Pak 4.0 ton Hydronic system with a Unico 1218 for the basement on Zone 2 and a Unico 2430  on zoned 1 for my upper two floors. I have had the Nest for year and I had to replace the exterior unit (Space Pak) due to a freon leak on the exterior unit. 

Anyway worked great all summer but now that I am in the winter months, the heat is not running on the 2430 unit. The 1218 runs fine, turns on circulator etc. and blows warm air. The 2430 will turn on, and start to blow air for about 5 seconds and shuts down the fan. It show that is still running at the thermostat as well as the heat is showing is is creating it but between the fan and circulator it is not working. 

I have tested all the points and I have 28 volts, I have tried to wire the same as wiring set up as the basement but no luck. I have jumped the wires and it works as long as I hold the wires one. I have even gone to the thermostat and put the two wires together and it runs. I am very confused as one works and one does not. Now the basement is a plan jane thermostat with 5/2 day programing. I did try another thermostat and got the same results. 

If anyone has an idea I would appreciate it. 

[jenniffert]

Hi wg8569,

Thanks for reaching out to the community! I apologize for your experience with the heating mode not functioning in Zone 2 and only operating in Zone 1. I'm happy to assist you.

Since you've already attempted a few workarounds, I'd like to ask for more details so I can assist you more effectively:

• What is the model of your Nest thermostat? Here’s a helpful article about how to identify your thermostat model.
• Does the issue happen on heating only, cooling only, or both?
• When was the last maintenance and cleaning service performed on your HVAC system?
• Could you please share a photo of the thermostat's wiring installation?

In the meantime, I’d suggest checking the following:

• Ensure the wires are fully inserted into the terminal and the connector buttons are securely pushed down. This guarantees proper wire connections. I also recommend cleaning the wires with a paper towel, as dust can sometimes prevent the base from recognizing the wires. You can check out this article for more information: Troubleshoot strange heating or cooling behavior. Important: Before touching any wires, turn off the power to your HVAC system at the breaker box. 

Please keep me posted.

Best regards,

Jenniffer