Heating & Air Conditioning Building a Home

Help with heating problem (NEST)

5 years ago

Hi, I moved into my new house about 3 weeks ago and have had continuous problems with my Nest thermostat. The most common problem is the zone calling for heat even though the temp is turned down, AND in these cases the zone valve LED is off but the zone is OPEN. See pictures.

This has occurred repeatedly on 2 of my 4 zones, and to date, my plumber has made about 6-7 visits and checked wiring, added another transformer, and replaced the zone valve heads. Most recently, we swapped out the NEST for a regular old Honeywell thermostat, and now it all works perfectly! So, the NEST is doing something funny on 2 zones.

Again the recurring problem is as follows: temperature set for 65 but actual temp is 70. It should not be calling for heat, yet heat is coming up through the baseboard. What's happening is that zone valve is open, yet LED is off. Please see pictures. Without NEST, everything is working fine.

From my POV, it seems like my heat is running normally with the NEST, but when it comes time to shut off, it only flips of the LED but doesn't close the valve.

Thank you!

Featured Answer

mike_home

5 years ago

I am happy to hear you were able to fix the problem with a simple wiring connection. I don't understand why Google Nest does not warn its customers that their thermostat may not work reliably without a C wire. It would save homeowners and professional installers a lot of grief.

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Comments (6)

mike_home
5 years ago
Does the Nest thermostat have a wire connect to the C terminal going back to the boiler's control board?
Paula Giglio
Original Author
5 years ago
Hi mike_home, thanks for offering to help. The nest is only connected to 2 wires: a white wire going to W1 and a red wire going to RH. I thought you didn't need to connect to the C wire with the Nest.
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mike_home
5 years ago
The Nest thermostat has a WiFi radio which needs power. The RH is the 24 V power. The C is the ground connection. If no C wire is present, the ground is supplied by another connection. In your case it is W1. It doesn't work with every control board. I recommend you install a C wire connection to fix the problem. If you call Google Nest they will probably give you the same advice.
Paula Giglio thanked mike_home
Paula Giglio
Original Author
5 years ago
OK, thank you Mike. I thought you didn't need the C wire, but maybe that's it. Will try that.

Paula
Paula Giglio
Original Author
5 years ago
@mike_home, thank you! We tried connecting the C wire and that fixed the problem. In the past, I've had plumbers and electricians both tell me that you don't need the C wire with the Nest, but apparently they were incorrect! And, without the C wire, the failure mode is very weird and inconsistent. Thanks again.