Heater Not Working in the House? What to Check First

Safety first. If you smell gas (a rotten-egg odor) or a carbon monoxide alarm sounds, leave the house right away and call your gas utility or 911 from outside. Do not flip switches, use a phone indoors, or try to find the leak.

Check these first

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Set the thermostat to Heat, raise it a few degrees above room temperature, and replace the batteries.
Check the breakers for the furnace or air handler, and for the outdoor unit if you have a heat pump. Reset a tripped breaker once only.
Make sure the power switch at the furnace or air handler is on.
Replace the filter if it is clogged.
Open all supply registers and uncover the return grilles.
Look for a blinking light on the furnace control board and write down the flash pattern.
If you have a heat pump, clear snow, ice and debris from around the outdoor unit.

Still not working after these? That is the point to bring in a licensed technician.

Request a call back Repair or replace?

First, work out which heater you have

What you see	System
Metal cabinet indoors with a gas pipe and a vent or flue pipe, warm air from registers	Gas furnace
Indoor cabinet with no gas pipe and no flue, warm air from registers, no outdoor unit running in winter	Electric furnace
Outdoor unit that runs in winter, thermostat may show "Aux" or "Em Heat"	Heat pump
Radiators or baseboard pipes, no air registers	Boiler

If the outdoor unit runs in winter, go to heat pump not heating. For a gas furnace, keep reading.

What it usually means

A heater that does nothing at all usually has a control or power problem: the thermostat, a breaker, a switch or a safety lockout. A heater that runs and blows cool air has a heat-production problem: ignition on a gas furnace, heating elements on an electric furnace, or the outdoor unit on a heat pump. Heat in some rooms and none in others points to airflow or ductwork, with the heater itself working.

Likely causes, most common first

Thermostat settings or dead batteries. This includes a thermostat left on Cool or Off after a mild spell.
Power interrupted. A tripped breaker, the furnace switch turned off, or a loose furnace door.
Clogged filter. The furnace overheats and shuts its burners off to protect itself.
Ignition fault on a gas furnace. A worn ignitor, a dirty flame sensor or a pilot that has gone out. The step-by-step version is in furnace not turning on.
Condensate or vent blockage on a high-efficiency furnace.
Gas supply. A closed gas valve, an empty propane tank or an interrupted utility service.
Failed motor or control board. The blower, the inducer or the board itself.

What a technician will do

The technician confirms the thermostat is sending a heat call, reads any fault code, and then tests the parts in the order the system uses them. On a gas furnace that means the inducer, pressure switch, ignitor, gas valve, flame sensor, limit switches and blower. On an electric furnace it means the sequencers and heating elements. You should come away with the name of the failed part, the reason it failed if one is known, and a written price.

Before the visit, write down what the heater does when the thermostat calls for heat, any blink code, when the filter was last changed and whether the problem started suddenly or built up over days. Those details shorten the diagnosis, and a shorter diagnosis usually means a smaller bill.

When it points to replacement

One failed part is a repair. Replacement is worth pricing when the furnace needs a heat exchanger, when it has needed several repairs in recent seasons, or when parts for it are hard to get. The furnace repair guide explains how to compare a repair quote with a replacement quote.

Common questions

Why is my heat not working but the fan is blowing?

The blower is running without a heat source behind it. Check that the thermostat fan setting is on Auto. If the air is still cool, a gas furnace likely has an ignition or overheating fault, and a heat pump may be in defrost or have an outdoor unit problem.

Why is the central heat not working in only some rooms?

Uneven heat usually comes from airflow. Look for closed or blocked registers, a clogged filter, or a disconnected or crushed duct in the attic or crawl space. Homes with zoning can also have a stuck damper or a failed zone thermostat, which a technician can test.

The house heater is not working after summer. Why?

The first cold night exposes problems that built up while the heater sat idle: a thermostat still on Cool, a filter loaded from cooling season, a pilot that went out, or an ignitor that finally cracked. Run the checks above, and book a tune-up before the next season starts.

Should I turn the heater off if it is not working?

If it is blowing cool air or cycling without heating, set the thermostat to Off until it is checked. That saves wear and stops repeated failed ignition attempts. If you smell gas or burning, leave the thermostat alone, get out and call from outside.

Next step

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Heater not working in the house? What to check first