If your heater isn’t working, start by checking the thermostat, breaker, and air filter. Most heating problems come from just a few common causes, and you can check several of them quickly without any tools. If you smell gas or a safety switch keeps tripping, stop right away and call a professional.
It’s frustrating when your heater won’t turn on during the first cold night, but the cause is usually easy to find. Each time a furnace starts, it goes through a quick checklist. If something goes wrong, the furnace stays off.
Below are the checks in the order a technician would run them, so you’ll know which to fix and when to stop.
Heater Not Working? What Should You Check First?
1. Thermostat settings and batteries
Make sure it’s set to Heat, with the set point a few degrees above room temperature. A blank screen usually means the batteries are dead.
If it stays dark after you replace the batteries, our thermostat repair and replacement service can test the wiring.
2. A tripped breaker or furnace switch
Your furnace has its own breaker and a service switch near the unit that looks like a light switch. In practice, we often find that switch bumped off by stored boxes.
Reset a tripped breaker once. If it trips again, leave it off.
3. A loose blower door
A small safety switch is under the front panel. If you don’t put the panel back properly after changing the filter, the furnace will not start.
4. A clogged air filter
A clogged filter blocks airflow and causes the furnace to shut off to prevent overheating. Trane suggests changing filters every 1 to 3 months, depending on how much you use your system. We explain filter sizes and how often you should replace your furnace filter.
If these four checks don’t bring the heat back, the problem is most likely inside the furnace.
Why Does My Furnace Start, Then Shut Off?
5. No gas or no ignition
Check that the gas valve handle runs parallel to the pipe, which means it’s open. Newer furnaces use a hot surface igniter that glows orange before the burners light.
Clicking with no flame usually means a failed igniter or gas valve.
6. A dirty flame sensor
This is one of the most common fall calls we see. The burners light, then cut out, because a soot-coated metal rod can’t confirm the flame.
7. A clogged condensate line
High-efficiency furnaces make water as they run. If the drain line clogs, a float switch shuts the system down. Water around the base is the clue.
8. Blocked vent pipes
These furnaces vent through two white plastic pipes on an outside wall. Snow or leaves over the openings will trip the pressure switch.
Which Heater Problems Can You Fix Yourself?
Here’s how we sort a heater not working into DIY fixes and pro repairs.
| What you notice | Likely cause | DIY or pro? |
|---|---|---|
| Blank thermostat | Dead batteries | DIY |
| Furnace is silent | Breaker, switch, or door | DIY |
| Weak airflow | Dirty filter | DIY |
| Clicking, but no flame | Igniter or gas valve | Pro |
| Flame lights, then dies | Dirty flame sensor | Pro |
| Water at the base | Condensate line | Pro |
| Runs, then locks out | Blocked vent | Clear vents, then Proo |
Anything involving gas, flame, or the control board requires a licensed technician.
When Is a Heater Not Working a Safety Problem?
Usually, a heater not working is just an inconvenience. These signs mean stop troubleshooting now:
- You smell gas or rotten eggs. Leave the house and call your gas utility from outside.
- Your carbon monoxide alarm goes off.
- A red reset button near the burners keeps popping out. That’s the rollout switch, and it trips for a reason.
- An electrical burning smell won’t fade.
Why 1-800-Plumber +Air for Heater Repair
Our technicians follow the same sequence you just read, so the fix matches the real cause. If your system is aging, we’ll tell you honestly whether repair is worth it.
Regularly checking your heater helps catch issues like dirty sensors or clogged drains before winter hits. If you ever need help, we’re here 24/7.
Final thought
If your heater isn’t working, the problem is often something simple, like a setting, switch, or filter. Start by checking these first four things. If your home is still cold, contact your local 1-800-Plumber +Air team or call 1-800-758-6237 anytime.
FAQ’s
Why isn’t my heater working?
Some common causes include an incorrectly set thermostat, a tripped breaker, a dirty air filter, or a dirty flame sensor. A clogged condensate line or blocked vent pipe can also shut down the furnace.
How do I fix a heater that isn’t working?
Check the thermostat, breaker, service switch,h and filter first. If the house is still cold, look for water at the base or blocked vent pipes outside. Anything involving gas or flame needs a pro.
How do I reset a furnace heater?
Turn off the service switch or breaker, wait about a minute, then turn it back on. If there’s a red reset button near the burners, press it only once. If it trips again, call a technician.
Why is my heater on but blowing cold air?
First, check that the thermostat fan is set to Auto, not On. On keeps the blower running between heating cycles. If it’s on Auto and still cold, the burners aren’t lighting.
Is a heater not working an emergency?
Yes, it can be urgent. For example, in freezing weather, cold rooms can freeze water pipes. If you smell gas or your carbon monoxide alarm sounds, act right away. In other situations, start with a few quick checks.