Safety first: Turn off power to the furnace/air handler at the breaker before removing the thermostat.

Check furnace power and fuse: Verify the furnace breaker and service switch are ON. Open the blower compartment and inspect the low-voltage fuse on the control board; replace if blown.
Inspect R and C at thermostat: Remove the Wyze display and confirm the R and C wires are fully inserted and clamped in their terminals. Re-strip and reinsert if necessary.
Measure voltage (advanced): With power restored and using a multimeter, measure AC voltage between R and C at the thermostat wall plate. You should see ~24VAC. If present but the screen is still blank, the thermostat display is likely failed.
Test with spare thermostat (if available): Temporarily connect a known-good basic thermostat to confirm the HVAC system powers a thermostat correctly.
Replace Wyze thermostat: If there is proper 24VAC at the wall plate and wiring is secure, replace the Wyze thermostat display assembly.

Thermostat screen is completely blank and unresponsive; HVAC system does not run.

Possible Causes