If your furnace is running but the house stays cold, it usually comes down to one of three things: the thermostat is set or wired wrong, airflow is choked off by a dirty filter or closed vents, or the furnace is not actually making heat. Here are the safe checks to make first, what the pattern is telling you, and when it is time to stop and call.
Before anything else, a few of these you can check yourself in a couple of minutes, with nothing more than your eyes and the thermostat. They solve a real share of no-heat calls, and even when they do not, they tell us something useful.
Make sure it is set to HEAT, the target temperature is above the room temperature, and the fan is on AUTO, not ON. Fresh batteries fix more no-heat calls than people expect.
A clogged filter chokes off airflow and can make a furnace overheat and shut its burners down. If the filter is gray and packed, replace it and give the system a few minutes.
Walk the cold rooms and make sure the supply vents are open and not blocked by rugs or furniture. Closing too many vents can actually make the whole system struggle.
There is a switch that looks like a light switch near the furnace, and a breaker in the panel. If either got flipped, the furnace will not run. Reset a tripped breaker once. If it trips again, stop and call.
Many furnaces have a small light you can see through a window without opening anything. A blinking code means the furnace is telling you what is wrong. Do not open the furnace cabinet to investigate.
How the furnace is misbehaving usually points at the cause. Notice which of these sounds like your house, because it is the first thing we will ask.
If the filter is clean, the thermostat is right, power is on, and it still will not heat, the next steps involve the burners, the flame sensor, the igniter, the gas valve, or the control board. Those are not guess-and-replace parts. We measure what the furnace is actually doing, find the real fault, and show you the fix in plain language before we touch it.
One safety note that matters. If you ever smell gas, see soot around the furnace, or a carbon monoxide alarm sounds, stop, get everyone outside, and call 911 from outside. See our furnace and carbon monoxide guide for exactly what to do.
A repair quote should follow a real diagnosis, not stand in for one. That said, when a furnace is well into its service life, parts are failing one after another, and the fix costs a meaningful share of a new system, replacement starts to make more sense than another repair. If you are at that point, we will lay out both paths honestly and let you decide. See heat pump vs gas furnace in Maryland if you are weighing what to put in next.
Usually one of a few things: the thermostat fan is set to ON so it blows between heating cycles, the furnace tripped a safety and stopped making heat, or the filter is so clogged the furnace overheats and shuts the burners down. Check the thermostat and filter first. If it keeps blowing cold, it is time to have it looked at.
It depends on what is actually wrong, which is why we start with a diagnosis instead of a number over the phone. You get the findings and a written price before any repair goes ahead, so there is no surprise on the bill.
If you smell gas, see soot, or a carbon monoxide alarm sounds, shut it off, get outside, and call 911 from outside. Otherwise a furnace that runs but will not heat is usually not dangerous, just broken, and running it hard can make the wear worse. When in doubt, turn it off and call.
Most furnaces run fifteen to twenty years with regular maintenance. Past that, repairs come more often and parts get harder to find, which is when replacing starts to make more sense than fixing.
That is called short cycling, which just means it starts and stops before it finishes a real heating cycle. A dirty filter, a bad flame sensor, or an oversized furnace can all cause it. It is worth checking, because short cycling wears the furnace out faster.
Tell us what your heating or cooling system is doing. Include the service address and any useful photos taken from a safe distance.
Clear answers. Clear scope.
Know what you are approving.
Verified Google reviews, 5.0 from 44
"I had a water leakage in my HVAC unit and Jay came out and did an amazing job on the repair. It took him longer than expected and he was working later into the night but made sure everything was done properly and efficiently. Super grateful for Jay's hard work and will definitely be reaching out for any future HVAC repairs I need!"
Google"Jay and Jacob were amazing getting my HVAC system operating correctly. Other companies probably would've said I need a new system but they took the time to diagnose the issues, addresses them, and went above and beyond getting the system in tip-top shape. They easily put 40 hours into the project to get it in order working well into the evenings and nights to ensure the home is comfortable. They will be my go-to for home services moving forward."
Google"Finally, someone reliable, professional, and who does outstanding work to rely on for all of our home repair needs. We have tried countless individuals and companies for the maintenance upkeep of our home for years, but never one that we would call back a second time. That was until Jay sent over his folks and now we have our trusted go to home services team for everything in the future. Thanks for the peace of mind Jay!!"
Google