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Furnace short cycling with nest gen 3

Fillyfilm
Community Member

I have a 5 wire system Y1, G, Rc, W1, Rh

Dual transformers. Central forced air and gas base board 

i installed the gen 3 nest thermostat on one of the 3 zones of heat the furnace would power on for 5 minutes, quickly shut off, then turn back on. I added a C wire from the AC unit. Same issue

i then removed all AC wires (Y1, G, Rc, C) from the nest and just kept W1 and Rh, no short cycling. I then reattached all wires. Short cycling again. I tested just removing Rh and keeping all other wires (Y1, G, Rc, C, W1), no short cycling

I don’t really understand what the issue is.

My question is do I have to use the Rh wire at all? Can I keep the Rh wire disconnected from the nest at all times? Could the C and Rc from the AC ever damage the furnace motherboard or anything like that? Is there another solution?

8 REPLIES 8

Azúl
Community Member

Upvoting as I have this exact same issue and question.

Jake
Community Specialist
Community Specialist

Hey all,

 

Apologies for the delayed reply. I wanted to follow up and ensure you are good to go. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

Jake
Community Specialist
Community Specialist

Hey all,

 

I want to ensure you are good to go, and everything is working properly. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity. 

Best regards,
Jake

Lizzyf
Community Member

Mine doesn’t have ax but I have the same short cycling problem then my furnace started making a repetitive almost low revving noise. It’s a new furnace within the last 7 months and the nest was installed 5 days ago

Azúl
Community Member

This issue still persists. When I have Y1, G, Rc, W1, Rh, and C all connected, the boiler short cycles. The A/C did not have this issue during the summer. I have gone back to a regular thermostat in the meantime to protect my boiler.

duckwingduck
Community Member

I have been having the same issue as well. What is the recommended solution?

I called a nest pro. He wired an isolation relay which fixed the problem. It cost a few hundred dollars but now I don’t have to worry about killing my boiler

Sparkie
Community Member

Just bought the 3rd Gen learning thermostat. Furnace A/C would run for a minute then start repetitive cycling. My thermostat cable is 4-wire, with no Common. So I bought the NEST power connector, installed per an on-line video, but with no improvement. Here's the catch. The Power Connector is configured for Heat, Cooling, and Heat+Cooling. You must choose the correct wiring configuration among the 3 choices. I initially wired for Heat per the video, when it should have been Heat+Cooling. Changed two wires and life is good. Note the Power Connector has two terminals marked W/Y, meaning white or yellow. For Heat+Cooling, use the yellow.