How to Reset Your Furnace Safely (and When You Should Not)

Quick answer: To reset most furnaces, set the thermostat to Off, switch off the furnace's service switch or breaker, wait about 30 seconds, then turn the power back on and set the thermostat to Heat a few degrees above room temperature. Many modern gas furnaces have no single red reset button, so cycling the power is the reset. Reset once only. If the furnace locks out again, a part is failing and needs furnace repair. If you smell gas or a carbon monoxide alarm sounds, don't touch anything. Leave the house and call 911 or your gas utility from outside.

When the heat stops on a cold morning, "how do I reset my furnace" is one of the first things people search. A reset can genuinely fix a temporary glitch. It can also hide a real problem, or make one worse. This guide shows you how to do it safely and when to stop.

Before you reset: quick checks

Many "dead furnace" calls turn out to be something simple. Check these first:

1. Thermostat: set to Heat, several degrees above room temperature, fan on Auto, fresh batteries. See thermostat troubleshooting.
2. Filter: a clogged filter can make the furnace overheat and shut down. See the air filter guide.
3. Service switch: a light-style switch on or near the furnace. It's easy to flip off by mistake.
4. Breaker: look for a tripped furnace breaker in the panel.
5. Door panel: the blower door must be fully closed, or a safety switch keeps the furnace off.
6. Gas valve: the handle on the gas pipe should run parallel with the pipe.
7. Outdoor vents: on high-efficiency furnaces, clear snow, ice or leaves from the plastic pipes outside.

Fixing one of these may get your heat back without any reset at all.

How to reset a modern gas furnace (step by step)

1. Set the thermostat to Off.
2. Turn off the power at the furnace service switch or the breaker.
3. Wait about 30 seconds. This lets the control board fully clear its lockout.
4. Turn the power back on.
5. Set the thermostat to Heat, a few degrees above the room temperature.
6. Watch and listen. A normal startup goes: inducer fan starts, igniter glows or sparks, burners light, and after a short delay the blower starts pushing warm air.

Give it a few minutes. If warm air comes out and keeps coming, you're done, but keep an eye on it.

What about the red reset button?

Some equipment has a button you can press:

• Blower motor reset: a few motors have a small thermal reset. If it trips, the motor overheated, often because of a dirty filter or a failing motor.
• Oil burner reset: oil furnaces and boilers have a red button on the burner's primary control. Press it once only. Pressing it repeatedly can pump oil into the combustion chamber, which can be dangerous to light. If it locks out again, call.
• Rollout or limit switches: some have manual resets. They trip when flames or heat go where they shouldn't, so a tripped rollout switch is a warning sign. Don't reset it more than once. See cracked heat exchanger signs.

If you're not sure what a button does, leave it alone.

Read the blinking light first

Most modern furnaces have a small window with an LED on the control board. Before you reset, count the blinks and match them to the chart on the inside of the furnace door. Write the code down. A reset clears the fault, so if you skip this step, the clue disappears. Common codes point to:

Exact meanings vary by brand, so always use the chart on your own furnace.

When a reset is fine and when it isn't

A reset is reasonable when:

• The power flickered or there was an outage
• The thermostat lost power or was replaced
• The furnace ran normally until a single lockout

Don't reset, and call instead, when:

• You smell gas: leave the house and call 911 or your gas utility from outside
• A carbon monoxide alarm sounds: get everyone out and call 911. See carbon monoxide detector beeping.
• You smell burning plastic or see smoke or scorch marks
• It has already locked out once today
• Water is pooling around the furnace (see furnace leaking water)

Why it keeps locking out

If your furnace needs resetting every day or two, something is wearing out. The usual suspects:

• Dirty flame sensor: the burners light, then shut off after a few seconds. See dirty flame sensor.
• Failing igniter: there's no glow or spark, or the burners light only some of the time. See furnace won't ignite.
• Overheating: a dirty filter or closed vents trip the limit switch. See furnace keeps shutting off.
• Venting or condensate problems: blocked pipes or a frozen drain line. See frozen condensate line.
• Control board or power issues, often after storms

Each reset on a failing part adds wear. A repeated lockout is a signal to book a repair before the furnace fails on the coldest night.

Resetting after a power outage

Storms and outages are common at the Jersey Shore. When power comes back:

1. Give the furnace a few minutes. Many restart on their own.
2. Check the breaker and service switch.
3. Power cycle it once if needed.
4. If the thermostat's screen is blank, check its batteries or power.
5. If it still won't run, call. Power surges can damage control boards.

A whole-home surge protector is worth asking about if outages are frequent where you live. See storm prep for HVAC.

Staying safe while you wait

• Use only indoor-rated space heaters, kept away from anything that can burn. See space heater safety.
• Never heat your home with an oven, stove or grill.
• If it's freezing outside, open cabinet doors under sinks and let faucets drip. See no heat and frozen pipes.
• Keep carbon monoxide alarms working on every level.

What a technician does differently

Instead of clearing the fault, we find out why it happened:

1. Read the stored fault history
2. Watch a complete heating cycle
3. Test the flame sensor, igniter, switches and gas pressure
4. Check venting, the condensate drain, airflow and temperature rise
5. Test for carbon monoxide
6. Explain what we found and give you an upfront price before any repair

See what affects furnace repair cost and emergency furnace repair: what to expect.

Prevent the next lockout

• Change the filter on schedule
• Keep supply vents and returns open
• Clear snow from outdoor vent pipes after storms
• Book a yearly heating tune-up: our $89 tune-up includes cleaning and safety checks (terms apply)

The Prime Comfort Club covers one heating and one AC tune-up a year for $19/month, with priority scheduling and 10% off repairs (terms apply).

Furnace repair near you, 24/7

Our own licensed team repairs every furnace brand across all 153 towns in Ocean, Monmouth, Burlington and Middlesex counties, including Toms River, Brick, Howell and Edison.

Reset didn't work? Book online or call (732) 779-7106, day or night. New customers save $50 on their first repair (terms apply).