Symptoms
- No response to touch or buttons
- No lights, no beeps
- HVAC not turning on
Likely causes
- CommonDead or missing batteriesMany smart and programmable thermostats still use batteries as backup power.
- CommonTripped breakerLoss of building power cuts the low-voltage transformer that runs the thermostat.
- CommonBlown low-voltage fuseA short somewhere in the system can blow a small fuse and cut power.
- PossibleFailed C-wire connection on smart thermostatsSmart thermostats need constant power and stop working if the C-wire comes loose.
- Less commonInternal failureAge or a power surge can kill the thermostat's electronics.
What to do
- Replace batteries if the thermostat uses them.
- Check the breaker panel for the HVAC circuit and reset any tripped breaker.
- Remove the faceplate and check that all wires, especially the one labeled C, are firmly connected.
- Look for a reset button on the thermostat or its base plate and press it if present.
- If it's a smart thermostat, try removing it from the wall plate and reconnecting it after 30 seconds.
- If nothing revives it, the thermostat likely needs replacement.
Tools and parts
- Screwdriver
- Flashlight
- Fresh batteries
Replacement thermostatSearch: “programmable or smart thermostat”
When to call a pro
Call an HVAC technician if you're not comfortable working with low-voltage wiring or the problem isn't power-related.
Safety
Use caution
Shut off power at the breaker before removing the thermostat from the wall.