What should I do if my furnace is not heating?

What this symptom usually means

A furnace that is not heating is different from a furnace that is blowing cold air all the time or one that will not start at all. With this symptom, the heating call is usually reaching the equipment, but the furnace is failing somewhere in the heat-making sequence: draft starts, ignition is attempted, burners drop out, safety switches open, or warm air never makes it to the rooms. That is why homeowners often report the system running while the house temperature barely moves.

How to narrow it down by what you can observe

If airflow feels normal at the vents but the air is room temperature or only briefly warm, ignition failure, flame-sensor problems, or a limit shutdown are common suspects. If airflow is weak and the house is cold, the problem leans more toward blower performance, duct restrictions, a stuck zone damper, or the furnace overheating and shutting the burners off early. If you notice water around a condensing furnace, ice at the intake or exhaust, or a new humming or rattling noise before shutdown, condensate drainage, venting, inducer, or pressure-switch faults move higher on the list. If only one room or one zone is cold while the rest of the home heats, the furnace itself may be working and the fault may be in dampers, branch ducts, or airflow balancing.

What happens on a service visit

A technician will usually verify the full call-for-heat sequence from the control board outward: inducer start, pressure-switch proof, igniter operation, burner ignition, flame-sensor signal, blower timing, temperature rise, and whether any limit or rollout switches are opening. On high-efficiency models, they will also inspect condensate traps, drain tubing, vent piping, and pressure ports because a small blockage there can stop heating completely. If one room or zone is the issue, they may check damper operation, static pressure, and whether the furnace is delivering adequate warm air before it enters the duct system.

What affects repair cost

Costs depend heavily on which step of the heating sequence is failing. Common ignition-related repairs such as a flame sensor cleaning or replacement are often at the low end, while igniters, pressure switches, draft inducer motors, control boards, blower motors, or zone damper repairs are progressively more expensive. Typical 2025-2026 US repair ranges are roughly $170-$575 for a flame sensor service, $170-$575 for an igniter, $170-$575 for a pressure switch, $500-$1,575 for an inducer motor, $500-$1,575 for a control board, and $500-$1,575+ for blower or zoning-related work, depending on access and furnace model.

When to schedule service soon

If the furnace is repeatedly trying to heat but the home remains cold, do not keep forcing long recovery periods by cranking the thermostat much higher. Repeated failed ignition attempts, overheating trips, or short cycling can add wear and sometimes turn a smaller repair into a larger one. Schedule service soon, and if you also smell gas, get carbon monoxide alarms, see smoke, or notice an electrical burning odor, leave the building and call the gas utility or emergency services from outside.