topic Re: Thermostat Not Detecting R Wire. in Nest Thermostats

Thermostat Not Detecting R Wire.

Watson1 — Sun, 17 Nov 2024 05:01:04 GMT

My 2-wire gas heater works (if I touch the two wires together it turns on).

When I plug those wires into W1 and Rh I get E74 error and the Nest refuses to exit error mode.

I also have a 24V C-wire transformer that works. When I plug that into C and Rc/Rh I get the error that there’s no power on the R’s too. When I go to the ‘Power’ menu section it says the thermostat is powered by 24V. But I still have the no R errors. Why is this happening??

Re: Thermostat Not Detecting R Wire.

GBD — Mon, 18 Nov 2024 18:31:43 GMT

Is it possible that you have the two wires backwards? When I removed an old standard thermostat and installed my Nest Thermostat (2020), it didn't work at first until I switched the wires.

Re: Thermostat Not Detecting R Wire.

kcruzgonzalez — Wed, 20 Nov 2024 20:27:07 GMT

Hi Watson1,

Thank you for posting in the community. I'm sorry that you're having troubles with the R wire on your thermostat. I understand how frustrating this can be. I'm here to help.

Before I begin, I need to ask a few questions for further assistance:

What model of thermostat do you have?
What HVAC system do you have?
When did the inconvenience start?
What's the current wiring configuration?
What's the old wiring configuration?
When did you install the thermostat?
In addition to twisting the RH and W1 wire, have you tried other troubleshooting steps?

Please, also, let's try the steps in this guide:

Wires must be firmly connected to the terminals. Ensure at least ¼ to ½ inch of the copper wire is exposed, straight, and inserted fully into the correct connectors. If needed, strip and reinsert the wires. If necessary, strip and reinsert the wires.
Wires that are too thin (smaller than 18 gauge) won't work with the Nest Thermostat. A Nest Pro or local technician can replace them if necessary.
The Nest Thermostat needs 18 to 22 gauge solid-core copper wires. Stranded wires are incompatible. If you have stranded wires, a Nest Pro or local technician can replace them.
Note: If you feel comfortable, please check the voltage of the RH wire using a voltmeter. The normal readout should be somewhere between 20 and 30 V (24 V is most common).

Please keep me posted. I'll look forward to your response.

Regards,

Kevin

Re: Thermostat Not Detecting R Wire.

Watson1 — Wed, 20 Nov 2024 21:46:38 GMT

You were half right - I was using a DC transformer instead of AC.