TP-Link Kasa
No Power to Thermostat
Thermostat display is completely blank and unresponsive
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Tripped furnace/air handler breaker, Blown low-voltage fuse on control board, Disconnected R or C wire, Failed 24V transformer
How to Fix / Troubleshooting
Safety: Turn off power at the main panel before opening furnace panels.
- Check breakers: Verify the furnace/air handler and any dedicated HVAC breakers are ON. Reset if tripped.
- Inspect furnace door switch: Ensure the blower compartment door is fully closed and engaging the safety switch.
- Check low-voltage fuse: On the furnace control board, inspect the small automotive-style fuse. Replace if blown, but investigate for shorts in thermostat wiring first.
- Verify R and C wiring: At the thermostat backplate, confirm R and C wires are connected and not loose or broken.
- Transformer test (advanced): With power on and a multimeter, measure between R and C at the furnace board for ~24 VAC. If no voltage, the transformer or internal protection is faulty and requires a technician.
- Replace thermostat: If 24 VAC is present at the thermostat wires but the display remains blank, the thermostat is likely defective and should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Furnace Control Board Fuse / 24V Transformer / Thermostat Assembly
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