Thermostat Not Detecting R Wire.

[Watson1]

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??

[GBD]

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.

[Watson1 · Accepted solution]

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

[kcruzgonzalez]

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