Thermostat on 2 wire boiler w/ext 24vAC

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So… Navien NHB-110 boiler with TT connection only. W / R(H) application only. Speaking to Navien the system only requires voltage across TT [ W/Rh] to provide the board with the command to close the contactor and turn on the boiler. Obviously the Wyze Thermostat [WT from now on] requires a common voltage. Reviewing everything and removing the boiler from the equation:

W + RH to the boiler TT landing point
RC + C coming to and from the AC adapter to power WT

Boiler is the only thing in this system

I’m seeing a constant 13v +/- across W/RH _ Just having the WT on the wall. Is this a wire landing issue using ext 24vAC for power or this a WT internal issue?

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TT generally doesn’t need external voltage, just a closed circuit. IIRC, the wyze has some diode leakage between Rh and Rc when in external powered mode, so if you wanted a completely isolated contact between Rh and W, you would need an external relay, but that’s generally only an issue in millivolt systems. otherwise the wyze should work for your application.

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That’s what I figured as well, but dio leakage at 13volts???

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Did you measure AC or DC on your meter? The control voltage is AC, so you should measure AC for an accurate reading.