Can Thermostats Go Bad?
What this costs
| Option | Job | Low | High |
|---|---|---|---|
| Replace | Thermostat Replacement | $100 | $510 |
Signs it may be the thermostat
These signs are our own checklist, not from a source. DOE, Carrier and Bryant list the causes to check, but not this list.
- The screen is blank even with new batteries.
- The reading doesn't match a separate thermometer placed next to it.
- The heat or AC doesn't respond when you change the setting.
Check before you buy a new one
- Mode: on Cool or Heat, with the setting past room temperature. Bryant and Carrier both start here.
- Fan: Bryant suggests Auto.
- Batteries: Carrier lists dead batteries first.
- Heat sources nearby: DOE says lamps and TVs near the thermostat cause longer run times.
- Power: check the breaker for the furnace or air handler.
Could it be something else?
We expect a blank thermostat can mean the system lost power, not that the thermostat failed. Carrier also lists loose wiring. If you've checked the basics, we recommend having a technician test whether the thermostat is sending a signal to the system. You can read our answer about replacing one yourself. EPA says mercury thermostats need proper disposal, so don't throw one in the trash.
Thermostat Not Working? Blank Screen and Other Fixes
Common questions
Can a thermostat affect the AC?
Why does a bad thermostat run my AC all the time?
Related questions
- Are GFCI Outlets Required in a Garage?
- Can a Breaker Go Bad Without Tripping?
- Can a Light Switch Cause a Breaker to Trip?
- Can a Roof Leak Be Fixed From the Inside?
- Can a Water Heater Leak Carbon Monoxide?
- Can Breakers Trip for No Reason?
- Can Garage Door Springs Kill You?
- Can GFCI Outlets Go Bad?
Last verified 2026-11-04
- U.S. Department of Energy: Energy Saver 101, Home Cooling — Thermostat might need new batteries or replacement; make sure it's reading the correct temperature.
- Carrier: Furnace not turning on — Dead batteries or loose wiring as thermostat problems.
- Bryant: Why is my AC not working? — Confirm Cool mode, set temperature and fan on Auto.
- U.S. Department of Energy: Top 11 things you didn't know about saving energy at home, summer edition (June 8, 2012) — Lamps and TVs near the thermostat affect how long AC runs.
- EPA: Mercury in consumer products — Mercury thermostats need proper disposal when replaced.
General information, not professional advice. Conditions, codes and prices vary. Turn off power, gas or water before any work, and hire a licensed professional when in doubt. Cost figures are our estimates, not quotes.