Thermostat screen is blank

Symptoms

• Screen shows nothing at all
• No backlight even when tapped
• HVAC system not running
• Worked fine yesterday

Likely causes

• CommonDead batteriesBattery-powered thermostats go blank when cells run low, often with no warning.
• CommonTripped breaker or blown fuseThe furnace or air handler circuit, or a small fuse on the control board, powers many thermostats.
• PossibleFurnace switch turned offA wall switch that looks like a light switch often kills power to the furnace.
• PossibleLoose or disconnected wireA wire can slip out of its terminal during cleaning or other work nearby.
• Less commonFailed thermostatElectronics can simply fail after years of use.

What to do

1. Replace the batteries with fresh ones, even if the old ones seem fine.
2. Check your home's breaker panel for a tripped breaker labeled furnace, AC, or air handler and reset it.
3. Look for a switch near the furnace that looks like a light switch and make sure it is on.
4. Check for a small blown fuse on the furnace circuit board, usually a glass tube near the transformer.
5. Remove the thermostat faceplate and check that wires are seated firmly in their labeled terminals.
6. If power returns elsewhere but the screen stays blank, the thermostat itself may have failed.

Tools and parts

• Fresh batteries
• Flashlight

When to call a pro

Call an HVAC technician or electrician if resetting the breaker doesn't hold, or if you see burnt or melted wiring.

Safety