Digital thermostat mounted on a concrete wall
Generic photo: Alexander Mass · Pexels License

Furnace runs no heat (blower only or nothing)

Start with the board LED code, then work the call path: thermostat, 24 V, safeties, inducer, ignition, flame proving. Most no-heat calls end at a filter, a flame sensor, a pressure switch issue or gas being off.

Single source ~45 min moderateBrands: All

Before you start

  • If you smell gas: do not operate switches or the furnace, leave the building and call the gas utility from outside.
  • Make sure the home has a working carbon monoxide (CO) alarm; if it is sounding or anyone has headache/nausea, get everyone out and call 911 / the gas utility.
  • Turn off power at the furnace service switch or breaker before opening the burner or blower compartment; the door switch alone is not a lockout.
  • Gas-side diagnosis or repair (gas valve, gas pressure, burners, heat exchanger, venting) is for a licensed gas/HVAC technician only.
  • Never jumper or bypass a limit, rollout or pressure switch.

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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