Furnace Not Working? 8 Checks to Do Before Calling a Pro
Many furnace problems turn out to be simple, like a thermostat setting, a tripped breaker or a clogged filter. Here are eight safe checks to try before you pay for a service call, and the signs that mean you should call a professional right away.
By Pond.com editors Updated 3 min read
Quick answer
- Start with the thermostat; check it's set to heat, set above room temperature, and has working batteries.
- Check the furnace's power switch and your circuit breaker.
- A clogged air filter is one of the most common causes of poor heating.
- Make sure the furnace door is closed properly and vents aren't blocked.
- If you smell gas, leave the house and call your gas company from outside.
A cold house is stressful, and a service call can cost $100 or more before any repair. Before you book one, a few simple checks can often solve the problem.
This article is general information. If anything feels unsafe, stop and call a professional.
8 checks to try first
- Thermostat setting. Make sure it's set to "Heat" and a few degrees above the current room temperature.
- Thermostat batteries. A blank or dim screen usually means new batteries are needed.
- The power switch. Most furnaces have a switch that looks like a light switch on or near the unit. Make sure it's on.
- The circuit breaker. Check your electrical panel for a tripped breaker labeled for the furnace, and reset it once.
- The air filter. A clogged filter can make the furnace overheat and shut down. Replace it if it looks grey or dusty.
- The furnace door. Many furnaces won't run unless the front panel is closed firmly, because of a safety switch.
- Vents and returns. Open the vents in each room and move furniture or rugs off them.
- Outside vent pipes. High-efficiency furnaces vent through plastic pipes on an outside wall. Clear any snow, ice or leaves.
When to call a pro right away
- You smell gas or burning, or your carbon monoxide alarm goes off.
- The furnace keeps turning on and off in short bursts.
- You hear loud banging, screeching or grinding.
- The breaker trips again after you reset it.
- Water is pooling around the furnace.
- Nothing above has worked.
When you call
Tell the technician what you've already checked. It can save time and money. Ask about the cost of the diagnostic visit up front, and whether it's credited toward the repair. For how to find someone reliable, see how to choose an HVAC company.
Preventing problems
- Book a yearly tune-up before the cold weather, ideally in early fall.
- Change the filter regularly through the heating season.
- Test carbon monoxide alarms monthly, and replace their batteries yearly.
- Keep the area around the furnace clear. Don't store boxes, paint or cleaning products next to it.
Common questions
Common causes include the thermostat fan set to "On" instead of "Auto," a clogged filter causing the furnace to overheat and shut off its burners, or an ignition problem. Check the thermostat and filter first. If it still blows cold, call a technician.
Many filters need changing every one to three months during heating season. Check the filter's packaging, and change it more often if you have pets or allergies.
Some furnaces have a reset button, but pressing it repeatedly can cause damage or hide a problem. If the furnace keeps shutting off, it's safer to call a technician than to keep resetting it.