Thermostat emits a buzzing or humming noise, especially when calling for heat or cool

Warning: Turn off power before removing the thermostat.

• Step 1 – Check mounting:
  • Ensure the thermostat is firmly snapped onto the wall plate and the plate is securely mounted to the wall.
• Step 2 – Isolate source:
  • Listen closely to determine if the noise comes from the thermostat or the furnace/air handler.
• Step 3 – Inspect relays (advanced):
  • With the thermostat removed, look for loose or vibrating relay components on the PCB.
• Step 4 – Replace thermostat if relay is noisy or failing:
  • Persistent buzzing from the thermostat usually indicates a failing relay; replace the thermostat.