What to check when a furnace is not heating
Check the thermostat mode and temperature setting, note any unusual odors or sounds, and arrange qualified help when combustion or electrical concerns are present.
What to check first
Practical first steps
Check the thermostat's heat mode and setpoint; inspect an accessible filter; record any error code and whether the blower starts.
Safety: Stop and leave the building if you smell gas or suspect carbon monoxide. Never bypass a furnace safety switch.
- Write down the displayed room temperature, heat setting, and time the heating problem began.
- From normal living areas, note whether air moves at vents and whether the problem affects every room.
- Photograph only visible displays or labels; do not remove a furnace panel to find a code.
What changes the right next step?
Tell the technician whether heating stopped suddenly, became intermittent, or never started this season. Include recent thermostat changes and previous service paperwork; these observations do not establish the cause.
Questions to ask before paying for repairs
Which observations support the diagnosis? Does the visit include checking safe operation, not just restoring heat? What fault was found, which work is necessary, and how will operation be checked afterward?
Safety and limitations
If a carbon monoxide alarm sounds or you smell gas, leave the building and contact emergency services or the gas utility from outside. Do not relight burners, reset safety controls repeatedly, or attempt gas, combustion, or electrical work.
Sources and further reading
These references support general safety, maintenance, or estimate-comparison principles. They are not a diagnosis or a source of live local prices. Use your model-specific manual and applicable local requirements for equipment procedures.