Furnace Not Working?
Safety First, Then The Easy Fixes.

Step zero: rule out danger

If you smell gas, leave the house and call your gas utility from outside. See our gas line page for the full steps. If a carbon monoxide alarm is sounding, or anyone in the home has a headache, nausea or dizziness that eases when they go outdoors, get everyone out and call 911. Don't go back to troubleshoot. Furnaces are a leading source of CO in winter, and the gas is odorless.

1. The thermostat

Set it to Heat and raise the temperature at least five degrees above the room. Replace the batteries if the screen is dim or blank. If you have a smart thermostat, confirm it hasn't lost Wi-Fi or switched to an away schedule.

2. Power to the furnace

Furnaces have a light-switch-style power switch on or near the unit, often mistaken for a regular wall switch, and it gets flipped off during storage or when someone changes a filter. Check it. Then check the breaker for the furnace in your panel. One reset is fine. If the breaker trips again, leave it off and call.

3. The filter

A clogged filter restricts airflow, makes the furnace overheat and shut down on its safety limit, and then restart again a few minutes later. If your furnace heats briefly and quits, check the filter first. Replace it if it's gray and you can't see light through it.

4. Vents and returns

Make sure supply registers and return grilles aren't blocked by furniture, rugs or closed dampers. Closing too many vents raises pressure in the ductwork and can cause overheating.

5. Furnace gas valve

Confirm the gas shutoff valve at the furnace is parallel with the pipe, which means open. If you're unsure whether your gas is on, check another gas appliance such as the stove. If none works, there's a gas supply problem and you should call the utility.

6. High-efficiency furnaces: look at the drain and the pipes

High-efficiency furnaces make acidic condensate that drains away through a small line. If that line clogs or freezes, a safety switch stops the furnace. Look for water pooled around the unit or a full drain trap. They also pull combustion air and exhaust gases through white PVC pipes that exit the house wall or roof. Heavy snow, ice or drifting can block these pipes, and a blocked pipe will shut the furnace down. Clear snow and ice from the outside openings by hand, but don't poke anything into the pipes or remove the pipe.

7. Read the blinking light

Many furnaces have a small window or panel where a status light blinks in a pattern. A label inside the door explains the codes. The pattern is useful to us if you tell us what it shows, even if you don't know what it means. Don't remove panels to look, as many furnaces cut power when the door is off and the cabinet holds live voltage.

What not to do

Don't bypass safety switches, hold down a gas valve, remove the burner compartment door while the furnace runs, or relight a pilot you don't know how to relight. Don't run a space heater unattended or use the oven for heat. Don't ignore a furnace that keeps shutting off, because the safety limits are there for a reason.

When to call us

If you've checked the thermostat, power, filter and vents and the furnace still won't run, or it starts and shuts down, it's time for a technician. A furnace repair visit starts with our $49 dispatch fee, applied toward any approved repair, and a written quote before work begins. Our phones are answered 24/7, so call if the house is getting cold at night.

Is it time to replace it?

Furnaces can last many years, but the repair bill matters. Read our guide on how long furnaces and air conditioners last in Utah, or see furnace installation if you're weighing replacement.

Related Homeowner Answers

• How often should you change your furnace filter? A clogged filter is behind many winter no-heat calls.
• How do I keep my pipes from freezing if the heat goes out?
• What should I set my humidifier to in winter?
• Why does my breaker keep tripping?