Thermostat Not Working? Quick Fixes & Replacement Cost

Many 'broken AC or furnace' calls turn out to be the thermostat: dead batteries, wrong settings, a tripped breaker or loose wiring. Thermostat replacement typically costs $85–$300 (about $200 on average), and a smart thermostat with professional wiring $250–$650.

Fix this weekDIY: Easy15–60 minutesPro: $85–$300

Last reviewed September 2026

Troubleshoot it now

Work through the checks one at a time. If this isn't your problem, the wizard moves on to the related causes.

Check 1 of 12Testing: Thermostat

Try this

Replace the batteries

Most blank thermostats just need fresh batteries.

Signs it's this problem

The display is blank or dim
The system doesn't respond when you change the setting
The room temperature doesn't match the setting
The system turns on and off very often

Why it happens

The thermostat is the switch that tells the system when to run. Dead batteries, a tripped HVAC breaker, dirt on old mechanical contacts, loose wires or a bad location near heat sources all make it misread or stop signalling.

Not sure? Run the heating and cooling problem finder

How to fix it, step by step

Tick each step as you go; your progress is saved on this device.

1.Replace the batteries if your thermostat has them.
2.Check the mode (heat, cool) and the setpoint, and turn off any schedule that may override it.
3.Check the HVAC breaker and the furnace or air handler's power switch.
4.Remove the faceplate (power off) and make sure no wires are loose.
5.If it's in direct sun or near a heat source, it may misread the room; relocate or shade it.
6.Still unresponsive? Replace it: photograph and label the wires before disconnecting.

Safety: Turn off power to the HVAC system at the breaker before touching thermostat wiring.

Thermostat Not Working? Quick Fixes & Replacement Cost cost

US national ranges for professional work, including labor and materials
Job	Typical cost
Replace a thermostat (average about $200)	$85–$300
Smart thermostat, professionally installed	$250–$650

Got a quote? Check if it's fair

Repair typeQuote amount (USD)

Typical professional price for this job: $85–$300

Common questions

How do I know if my thermostat is bad?

If fresh batteries, correct settings and a working breaker don't bring the system on, and wiring is secure, the thermostat has likely failed.

Can I install a thermostat myself?

Often yes, for simple systems. Smart thermostats may need a C wire, and heat pumps or multi-stage systems need careful wiring; a pro is safer there.