Thermostat Not Working? Blank Screen and Other Fixes

Quick answer

A thermostat that isn't working usually has dead batteries, the wrong mode or schedule, or no power because a breaker tripped or the furnace switch is off. Check those first. If the screen works but the system won't respond, the cause may be wiring or the equipment, and a technician can test it.

Key facts

Most common fix	Fresh batteries
Check next	Mode, fan setting, schedule, and holds
Blank screen with new batteries	Often means no power from the system
Smart thermostats	Check Wi-Fi and the app schedule
Leave for a technician	Wiring at the thermostat or the furnace

Why is my thermostat not working?

Most thermostat problems come down to power or settings. A thermostat needs batteries, power from your system, or both, and it only does what its mode and schedule tell it to.

Sometimes the thermostat is fine and the system isn't responding. Telling those apart is the first job.

What should I check on a thermostat that isn't working?

Don't pull the thermostat off the wall to check the wires. Loose or crossed wires can damage the system's control board, so leave wiring to a technician.

1Replace the batteries, even if the screen still shows something. Low batteries can cause odd behavior.
2Check the mode: Heat for heating, Cool for cooling. Set the temperature a few degrees past room temperature so it calls for a change.
3Set the fan to Auto.
4Look for a schedule, hold, or vacation setting that's overriding what you want.
5Check the breaker for your furnace or indoor unit. Reset it once if it's tripped.
6Make sure the power switch near the furnace or indoor unit is on. Many thermostats get their power from the system.
7Check that the furnace door is seated. A loose door cuts power to the system, and to thermostats powered by it.

Not sure what's wrong yet?

Start with the safe checks. Many problems are a setting, a breaker, or a filter.

Find your symptom Compare repair vs. replace

Repair first: we fix what can be fixed
You approve the price before work starts
Sources listed for outside facts

Is it the thermostat or my HVAC system?

What the thermostat shows, and what the system does, points to which side has the problem.

What you see	Likely points to	Next step
Blank screen, new batteries don't help	No power from the system: breaker, switch, door, or a blown fuse	Check the breaker and switch, then call.
Screen works and clicks, but nothing starts	Wiring, the control board, or the system itself	Call a technician.
Wrong temperature on the screen	Thermostat in sun or near a vent, or a failing sensor	Note where it sits. Call if it's far off.
System runs and won't shut off	A setting, a stuck relay, or wiring	Turn it off at the power switch near the unit, then call.
Smart thermostat offline	A Wi-Fi or app issue; it may still work at the wall	Check your Wi-Fi and the app.
Heat pump shows aux or emergency heat	A setting, or the heat pump not keeping up	See our aux and emergency heat guide.

When should I call about a thermostat problem?

Call when the batteries and settings check out and the system still won't respond, or when the thermostat and the system disagree.

New batteries and a reset don't bring the screen back.
The system won't shut off.
The breaker trips when the system tries to start.
You replaced the thermostat, and now something doesn't work right.

What will a technician check on my thermostat?

A technician tests whether the thermostat is sending the signal and whether the system is receiving it. That quickly shows which side has the problem.

Power at the thermostat and the control board
Wiring connections at both ends
Thermostat settings for your equipment: furnace, heat pump, or both
Fuses on the control board
Placement: sun, drafts, or nearby vents

Do I need a new thermostat?

Not always, because many thermostat problems are batteries, settings, a loose wire, or a system issue. We fix what can be fixed — and tell you straight when it can't.

If a new thermostat makes sense, we'll explain why and give you the price first. ENERGY STAR says homes with high heating and cooling bills, and homes that sit empty much of the day, can save with a certified smart thermostat. A new one only helps if it's set up right for your system.

Common questions

Why is my thermostat screen blank?

A blank screen usually means dead batteries or no power from your system. Replace the batteries first, then check the breaker, the power switch near the furnace, and the furnace door. If it's still blank, have it checked.

Why does my thermostat say it's heating but no heat comes out?

That usually means the thermostat is calling for heat but the system isn't responding. The cause may be wiring, a tripped safety switch, or a furnace or heat pump problem. Our furnace and heat pump pages list the next checks.

Can a thermostat read the wrong temperature?

Yes, sun, a nearby lamp, a supply vent, or a drafty door can make a thermostat read the wrong temperature. Moving a thermostat is a wiring job, so ask a technician if yours is in a bad spot.

Should I use Auto mode on my thermostat?

It depends on your system. For heat pumps, ENERGY STAR suggests choosing Heat or Cool instead of Auto so the system doesn't switch modes on unusual days. For the fan, Auto is the usual setting.

Why won't my thermostat turn off the system?

A system that keeps running after the thermostat is off may have a stuck relay or a wiring short. Use the power switch near the furnace or indoor unit to shut it off, and have it checked. Don't keep running it that way.

Can I install a smart thermostat myself?

Some homeowners do, but wiring differs by system, and heat pumps are easy to set up wrong. A wrong setup can cause short cycling or run backup heat more than needed. If you're unsure, have a technician install and set it up.