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Furnace Blower Runs Constantly

A blower that never stops is often set to Fan On at the thermostat, a stuck fan relay, or a control board fault. Check thermostat settings first; board or relay repairs typically run $100–$800.

Reviewed July 2026

What does furnace blower runs constantly mean?

The blower should stop when the thermostat is satisfied unless you've selected continuous fan mode. If the fan runs nonstop in Auto mode, a relay may be stuck closed or the control board may not be signaling the blower to shut off.

What usually causes furnace blower runs constantly?

Thermostat set to Fan Onmost common

Typical repair: $100–$400

Stuck blower relay on control boardcommon

Typical repair: $300–$800

Limit switch wired for continuous fanpossible

Typical repair: $150–$600

Find your exact error code

Select your furnace brand to jump to the code page for this symptom.

Tempstar7 FlashLimit or rollout soft lockoutLuxaire7 BlinksIgnition or flame-proving failure

What should I check first when furnace blower runs constantly?

  1. Set the thermostat fan switch to Auto and wait one full cycle.
  2. Replace thermostat batteries if settings seem stuck.
  3. Turn off power at the furnace switch for 30 seconds, then restore.
  4. If the blower still runs with power cycled, call a technician.

What a repair costs

A thermostat replacement typically costs between $100 and $400 nationally.

Typical repair cost
$100 – $400thermostat replacement
Where the money goes
Part $25–$250Labor $0–$375Typical labor time: 0.5–1 hrs

This is general information, not professional advice. Gas, electrical, and combustion repairs can be dangerous — when in doubt, call a licensed technician.