Thermostat not reaching temperature?

The thermostat is set higher (or lower) than the house ever gets. The cause is often a setting, a schedule or hold, a thermostat that reads the wrong temperature, or a dirty filter. If those check out, the heating or cooling system itself is probably the problem.

Not sure which one it is? Snap your thermostat and we’ll narrow it down.

Is the thermostat screen dark?

A blank display is a different problem, usually batteries or lost power. Thermostat blank screen

Likely causes

Wrong mode, or a schedule or hold overriding the setpoint
Most commonEasy DIY
The mode is set to Cool or Off in winter, a program lowers the temperature at this time of day, or a temporary hold is overriding what you set.
Thermostat reading the wrong temperature
CommonModerate DIY
It sits in direct sun, a draft, or near a vent or lamp, or it's on an outside wall. The reading differs from a separate thermometer in the room.
Dirty air filter
CommonEasy DIY
Weak airflow from the vents and a filter caked with dust, so the system runs a long time without moving enough air.
The heating or cooling system is struggling
CommonCall a pro
The thermostat is behaving, but the system short cycles, blows weak air, or doesn't make heat at all. Here the cause is the system, not the thermostat.
Normal heat pump behavior in cold weather
Less commonEasy DIY
A heat pump runs longer in cold weather, and its auxiliary heat comes on by itself to help. That's normal. Emergency heat is different: it's switched on by hand at the thermostat.
Failed thermostat
Less commonModerate DIY
Settings are right, the room is nowhere near the setpoint, and the system never starts or stops at the wrong time.
Part: $100–255 (replacement with labor)

Quick checks

Switch off the furnace or air handler power (or its breaker) before taking the thermostat off the wall or touching its wires. A thermostat for electric baseboard heat is line voltage (120 or 240 volts), not low voltage: turn the breaker off, and call an electrician if you're unsure. Don't bridge wires to "test" the system. Reset a tripped breaker once only.

Confirm the mode matches the season (Heat in winter, Cool in summer) and the setpoint is where you want it.
Cancel any hold and check the schedule for a setback at this time of day.
Check what's near the thermostat: sunlight, a draft, a vent, a lamp, or an outside wall. Compare its reading with a separate thermometer in the room.
Check the air filter and replace it if it's clogged.
On a heat pump, look at whether the thermostat shows Aux or Em Heat. Aux is the system adding backup heat by itself. Em Heat means someone switched it on by hand, so switch it back to Heat.

Sharpen the read

Diagnose your thermostat in seconds, for free

No account, no phone number. Fixology’s AI reads your photo and tells you what’s likely wrong, how worried to be, and whether it’s a DIY fix.

Snap one of these:

the thermostat screen (or blank face)
the wires behind the thermostat, with the power off
the furnace or air handler with its front panel and any status light

Add a note or more photos next. Nobody calls you.

When to call a pro

The settings, thermostat location and filter all check out and the house still won't reach the setpoint, the system short cycles or makes no heat, or the thermostat needs replacing. For lifespan and upkeep, see the thermostat guide. For the system itself, see furnace won't heat or heat pump not heating.

Typical cost: $114–321 for a typical thermostat repair (about $217 on average), though bills can run $50–500 overall. Replacing a thermostat with labor runs $100–255, and professional HVAC labor is about $50–100 per hour. A smart or Wi-Fi unit installed runs $185–600. If the cause is the heating or cooling system, the cost depends on that repair.

Sources: HomeAdvisor: How much does thermostat repair cost? (updated June 17, 2026), Fixr: How much does thermostat installation cost? (updated February 4, 2026)

After a scan, Fixology can also help you find pros near you.