Furnace not working: what to check first

Safety check before anything else

Some furnace problems are emergencies, not troubleshooting jobs. Leave the home right away and call 911 or your gas utility from outside if you smell gas (often described as rotten eggs), hear hissing near gas lines, or a carbon monoxide alarm sounds. Do not flip light switches, use phones inside, or try to find the source. Symptoms such as headache, dizziness, nausea or confusion that improve when you leave the house can be signs of carbon monoxide exposure; the CDC advises getting to fresh air and seeking medical help. Much of the Columbus area is served by Columbia Gas of Ohio for natural gas, so keep your gas utility's emergency number where you can find it.

Step 1: Check the thermostat

A surprising number of no-heat calls start at the thermostat.

1. Confirm the system is set to Heat, not Cool, Off or Fan only.
2. Raise the set temperature a few degrees above the current room temperature.
3. Replace the batteries if your thermostat uses them, especially if the display is blank or dim.
4. If you have a programmable or smart thermostat, check that a schedule or away mode is not overriding your setting.
5. Wait a few minutes. Many furnaces run a short start-up sequence before the burners light and the blower starts.

Step 2: Check power to the furnace

Gas furnaces still need electricity to run the controls, igniter and blower.

1. Find the furnace service switch. It often looks like a regular light switch on or near the furnace or at the basement stairs. Make sure it is on.
2. Check the electrical panel for a tripped breaker labeled furnace or HVAC. Reset it once. If it trips again, leave it off and call a technician.
3. If you have a high-efficiency furnace with a condensate pump, make sure the pump is plugged in.

Step 3: Check the air filter

A clogged filter restricts airflow, and many furnaces shut the burners off to protect themselves when they overheat. Pull the filter out and hold it up to a light. If you cannot see light through it, replace it with the size printed on the frame, with the airflow arrow pointing toward the furnace. Follow the manufacturer's guidance on how often to change it.

Step 4: Check the door panel and the status light

Most furnaces have a safety switch that keeps them off when the blower door is not fully closed. Make sure the lower panel is seated and latched. Many furnaces also have a small window with a blinking status light on the control board. The pattern is a diagnostic code; the meaning is usually printed on a label inside the panel door. Write down the pattern so you can tell the technician, but do not open the burner area or bypass safety switches.

Step 5: Check outdoor vent pipes after snow or ice

Many high-efficiency furnaces in Columbus-area homes vent through two plastic pipes on an outside wall or the roof: one brings in combustion air and one carries exhaust out. Heavy snow, drifting or ice can block them and the furnace will shut down. Carefully clear snow and ice from the pipe openings by hand. Do not put anything into the pipes. If you see frost buildup that returns quickly, or the pipes are damaged, call a technician.

Step 6: Check the condensate drain (high-efficiency furnaces)

High-efficiency furnaces produce water that drains through a small tube and trap, sometimes to a pump. If the drain is clogged or the line froze where it runs outside, a sensor can shut the furnace off. Look for water around the base of the furnace or a full condensate pump. If you find water near the furnace's electrical parts, turn off the furnace switch and call for service.

Step 7: Try one reset, then stop

After checking the items above, turn the furnace switch off for about 30 seconds and back on, then raise the thermostat. If the furnace starts and keeps running, keep an eye on it. If it tries to start and shuts off, cycles on and off repeatedly, makes loud banging or squealing noises, or produces a burning smell that does not go away after the first few minutes of the season, stop resetting it and call a heating technician.

• Columbus furnace and HVAC repair

Staying warm and protecting your pipes while you wait

Close curtains, gather in one room, and dress in layers. If you use a portable electric space heater, keep it at least 3 feet from anything that can burn and plug it directly into a wall outlet. Never use an oven, grill, camp stove or generator to heat the home. If the house will be cold for a long time, open sink cabinets on outside walls and let a cold faucet drip to reduce the chance of frozen pipes. If indoor temperatures become unsafe for anyone in the household, go somewhere warm.

• How to prevent frozen pipes in Columbus

Talk to a local provider

If your furnace still will not heat after these checks, call the number on this page to be connected with an independent local provider serving Columbus and nearby suburbs such as Dublin, Westerville, Hilliard, Grove City, Gahanna, Reynoldsburg, Upper Arlington and Worthington. Ohio Service Hub is a referral service, not a contractor. Availability, pricing and arrival times are set by the provider you speak with, so confirm them on the call. Calls may be recorded and may be routed to an independent local service provider.

Common homeowner questions

Government and primary-source references

• CDC — Carbon Monoxide Poisoning Basics
• CDC — Furnace Safety Fact Sheet
• U.S. Fire Administration — Heating Fire Safety
• Ready.gov — Winter Weather

External references support general guidance. They do not verify any specific contractor or provide a booking.