Why is my TH115-12VDC Master thermostat blank?

If your thermostat is blank, the first thing to do is to test to see if voltage is present at the rear of the thermostat. Verify that the power module power switches are in the ON position. Test for 12VDC across the 12VDC screw and the GROUND screw at the back of the thermostat. Here is a wiring diagram: https://www.warmlyyours.com/en-US/publications/MASTER-THERMOSTAT-W-POWER-MODULES-WIRING-DIAGRAM-B.pdf
If no power is reaching the thermostat, please test for 12VDC across the 12VDC and GND output at the front of power module base that is supplying power to the thermostat (the faceplate must be installed). If no power is present there, please inspect the circuit breaker in the breaker panel powering the power modules, and verify that the breaker is a non-GFCI type. If it is a GFCI breaker, replace it with a non-GFCI breaker. If there is power entering the thermostat and it is blank, it will need to be replaced. If power is getting to the power module and there is no 12VDC output to thermostat, the power module will need to be replaced.

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