Amazon Smart Thermostat
No 24V Power to Thermostat
Thermostat has no power, blank screen, does not respond at all
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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 24V control board fuse, Disconnected R or C wire at furnace, Broken thermostat cable between furnace and thermostat
How to Fix / Troubleshooting
Safety: Turn off the main HVAC breaker before opening the furnace/air handler cabinet.
- Check breakers and switches: Verify the furnace/air handler breaker is ON and any service switch on the unit is ON.
- Inspect control board fuse: Open the blower compartment and locate the low-voltage control board. Replace any blown 3–5A blade fuse with the same rating.
- Verify R and C at furnace: Ensure the thermostat R and C wires are firmly attached to the R and C terminals on the control board.
- Check at thermostat: Remove the thermostat and confirm the R and C wires are secure in the wall plate.
- Test with multimeter (if available): Measure between R and C at the wall plate; you should see ~24 VAC. If present but the thermostat is dead, the thermostat is likely defective.
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Repair Difficulty
Medium
3/5
Required Part
Furnace Control Board Low-Voltage Fuse
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