Wyze Stat turns off if interconnected HRV is turned on

New home with possession for about a month, new Wyze thermostat install. I’ve had one for 5 years at another property so am familiar with them. New home has electric high efficient furnace with A/C and an interconnected HRV as all new builds do now.

I performed the installation removing an Emerson non smart thermostat which appeared to be working fine but we’ve only needed A/C so far… 4 wires at the stat at W, RH (with a jumper between RH & RC) G and Y so the instructions said to install the C module which I did. I completed in install and finished the setup and tested both heat and cool and all was working fine.

This afternoon I walked by the stat and noticed it didn’t display the temp, pushed the button and nothing, checked the phone app and was reporting offline. Support topics stated power cycle, hold rotator button for 10 secs and reinstall but it was like the stat was dead. I started rechecking the wiring and at the furnace terminal strip there is a C wire terminal not previously connected to the furnace strip or thermostat, and a spare wire running up to the stat but not used on either end. The HRV is interconnected to the thermostat as per its wiring instructions intercepting the fan control G circuit.
After a bunch of double and triple checking I by accident hit the power switch on the HRV and turned it off and the Wyze stat came to life, push the power button back on for the HRV control and the stat turns off… I honestly can’t say for sure but the HRV must have been powered off when I did the install then it was turned back on at some time today.

Wondering if I should connect the additional spare wire running between the furnace strip and thermostat to the C on both ends, remove the C adapter and try again? It seems like now when the HRV is turned on the 24V drops to about 5V and not enough to power the stat, or the new furnace has an issue and the 24V supply is faulty and cannot support the two devices.

Thanks for any insight someone else may have!

1 Like

Pictures please. Both furnace side and thermostat side.

Sounds like you might have an under powered transformer running the system, not able to power all the devices that need to be powered from it: hrv, a/c contactor, furnace, and the thermostat.

If you’ve currently got a 20VA transformer, consider stepping up to a 40VA one, and if you currently have a 40VA, consider a 60VA… Note that bigger transformers are actually physically larger, so you may need to relocate it. Also be aware that the transformer is fed using line voltage, so if you’re not comfortable with working with line voltage, it’s best to have either an electrician or HVAC tech do it.

1 Like