Hi dr_56,
Thanks for reaching out and for being a step ahead of us. I'm sorry for the delay. I'd like to check it further. We need to identify if the wire is the one not delivering sufficient power to your Nest Thermostat, or the thermostat itself is the one not accepting the power from your wire. Do you have a voltmeter? If yes, are you comfortable using it?
Voltmeters and multimeters come in two types, analog and digital.
Analog models are no longer common, but they can still be found. They have a needle that moves across a window similar to a speedometer on a car. Digital models give a specific readout of the exact voltage measured. They can be extremely accurate and helpful for measuring voltage.
When using a voltmeter, you should turn the dial or switch to AC. AC current allows voltage to flow through the leads and allows the voltmeter to display an accurate readout.
To check voltage over any R wire: If your breakers are off, you will need to turn them on. On most multimeters, AC current is designated by VAC or V~.
Follow this guide on how to use a voltmeter:
- Set the dial to 200 VAC.
- If the multimeter doesn’t have a 200 setting, choose 100 or 250 VAC.
- The general rule of thumb is don’t set it too high (500+) or too low (50).Place the red lead on the R wire.
- Place the black lead on the other wire being tested (W1, Y1 or C).
- The normal readout should be somewhere between 20 and 30 V (24 V is most common).
- Suggestions to keep in mind if you get a very low readout or nothing at all:
- Test it one more time.
- Verify settings on the voltmeter are correct.
- Ensure that leads are plugged in properly.
Let me know how it goes.
Best,
Jenelyn
