Upstairs and Downstairs T3000 Thermostats Say "No Wires Detected"

I have an IQ2 panel that controls the system in my house. Two T3000 thermostats (one controls the upstairs zone and the other controls the downstairs zone) are connected to the IQ2 (via ZWave) and both of the thermostats have worked correctly for a few years. Now both thermostats are saying “no wires detected”, but they are connected the same way they have been from the beginning (I checked the wires at the back of each thermostat), the thermostats are powered up, the IQ2 and app aren’t detecting a problem, both thermostats are showing the correct target temp that’s programmed in the app, yet the AC is not turning on despite the temp being well above the target temp and the both thermostats being in “cool” mode (they’re actually in auto mode but the text on the thermostats is in blue).

Reason suggests there is a common wire or component in the attic that’s not allowing both thermostat to connect with the HVAC control board in the attic, right?

Any recommendations on what to do? I suspect that the thermostats as really saying is no load is detected on a specific wire. Which wire do you think is not working correctly?

I have a multimeter so I’d like to test those wires at the back of the thermostats. Which type of load should I check for? If the multimeter picks up no load, then I’ll go to the attic to see what’s going where they meet. I wonder if the HVAC control board is failing.

I would first test between R and C wires. Do you get 24VAC roughly?

If not, there may be an issue with the main HVAC terminals. If there is 24VAC, that may mean the Y wire is disconnected, or an issue at the AC.

I would also try deleting and resetting a thermostat, then reinstalling to see if the setup process picks up the right wires and if this issue still occurs.

Did you recently see any Safety Delay or Isolation Relay Required messages?

On the thermostat:

  1. Press the Menu button.
  2. Select SETTINGS.
  3. Select INSTALLER.
  4. Select CONTINUE.
  5. Select RESET.
  6. Select YES.
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No messages other than they both say no wires detected. I’ll check the wires tonight after work. When checking the wiring, first disconnect them from the thermostat, then check for the voltage?

For the R terminal 24VAC should always be coming across it. C completes the AC circuit and allows the Tstat to use 24VAC for power.

You often don’t need to remove them to test, but if you do, be sure to shut off power to the HVAC first before adjusting wiring, and avoid any shorts as this can damage the HVAC.

HVAC company came to fix it under warranty. Power surge from a storm on New Years eve blew something in the circuit board on the AC condenser. Then when the AC turned on for the first time this year a week ago, it below a fuse which causes the Tstats to say no wires detected. He said it’s the 5th one he’s fixed in the last month from that storm.

Thank you for following up and confirming!

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