Why Won't My Furnace Ignite?
A furnace that will not light usually has a thermostat problem, a tripped breaker, or a power switch someone flipped off. Sometimes a part has failed, like the ignitor or the flame sensor. Check the thermostat, the breaker, and the switch on the furnace first. If it clicks but never lights, stop there and call.
What stops a furnace from lighting?
Thermostat batteries or settings
A thermostat with dead batteries, or one left on COOL or OFF, never asks for heat. Fresh batteries, HEAT mode, and a temperature above the room rule this out in a minute. All of it is safe to do yourself.
Safe to check yourselfTripped breaker or furnace switch
Furnaces have a wall switch nearby that looks like a light switch, and it gets flipped off by accident more often than you would think. The breaker can trip too. Check that the switch is on and reset a tripped breaker one time only.
Safe to check yourselfDirty filter causing a lockout
After the furnace overheats a few times from a blocked filter, it locks itself out so it cannot keep trying. A fresh filter is safe to do yourself. If it stays locked out after a new filter and a thermostat cycle, the reset has to happen at the equipment.
Safe to check yourselfBlocked intake or exhaust pipe
A high-efficiency furnace breathes through two plastic pipes that end outside the house. Snow, leaves, or a nest blocking either one trips a safety and stops it lighting. You can look at those pipes outside and clear snow or debris away from the openings.
Safe to check yourselfBlocked drain
A high-efficiency furnace makes water every hour it runs, and that water drains away. A clogged drain trips a safety that blocks the burners. Look for standing water at the base of the furnace or a small switch that has tripped. Clearing the drain is a service visit, and spotting the water tells us a lot before we arrive.
Safe to check yourselfDirty flame sensor
The flame sensor is a thin metal rod that proves the burners lit. When it gets coated, the furnace lights, shuts the gas off within seconds, and repeats until it locks out. The sensor sits inside the burner compartment, so cleaning it is technician work.
Technician repairFailed ignitor
The ignitor is a fragile element that glows red hot to light the gas, and it wears out with age. When it cracks, you hear the furnace start its sequence and click, and no flame follows. Replacing it means working inside the gas train.
Technician repairGas valve or gas pressure problem
A failed gas valve, low gas pressure, or an empty propane tank leaves the furnace nothing to light. Noticing whether your other gas appliances work is fine. Anything past that, including touching valves or piping, belongs to a qualified professional or your gas utility.
Technician repairWhat can you check yourself?
- Put fresh batteries in the thermostat, set it to HEAT, and raise the temperature above the room.
- Check that the power switch on or near the furnace is in the ON position.
- Check the furnace breaker and reset it one time only if it has tripped.
- Change the air filter if it is dirty.
- Walk outside and clear snow, leaves, or debris away from the two plastic pipe openings.
- Look for standing water or a tripped switch at the base of a high-efficiency furnace.
Safety note: Never try to light the burners by hand or work on gas parts. If you smell gas at any point, leave the house and call your gas utility and 911 from outside.
When should you call for repair?
Call when the thermostat, the power switch, the breaker, the filter, and the outside pipes all check out and the furnace still will not light. Call without waiting if you hear clicking over and over with no flame. Call if it starts and shuts down within seconds several times. Call if it has locked out completely. Lighting problems live in the gas train and the safety circuit, and that is where homeowner work has to stop.
Boyds is two places at once. Nearer Clarksburg you are on public utilities. Head the other way and you are past the gas mains, on well and septic, with real distance between houses. Out there a propane furnace or a heat pump carries the winter. On a high-efficiency furnace the two plastic pipes come out through the side wall, and snow drifted over either one will stop it lighting. Clearing those two openings gets the furnace running more often than people expect.
Related questions
Why does my furnace click but not turn on?
Clicking with no flame means it is trying and failing. It could be a cracked ignitor, a spark that cannot light the gas, or a gas valve that is not opening. The furnace usually tries a few times and then locks out. Turn the thermostat down so it stops trying, then book a visit.
Why does my furnace light and then shut off after a few seconds?
Lighting and dying within seconds is the classic sign of a dirty flame sensor, the thin rod that proves the burners lit. The burners light, the sensor cannot see the flame, and the control board closes the gas valve to be safe. After a few tries the furnace locks out. That rod sits inside the burner compartment.
How do I reset my furnace?
The safe reset is from the outside. Turn the thermostat to OFF, switch the furnace power switch off for thirty seconds, then switch it back on and set the thermostat to HEAT. That clears many lockouts. If it locks out again after one reset, stop. Repeat resets push the furnace to keep trying something it has decided is unsafe.
Can cold weather stop a furnace from lighting?
Not directly, but it exposes the weak part. Deep cold is when tired ignitors crack, when snow blocks the two outside pipes, and when the drain on a high-efficiency furnace can ice up where it exits. That is why the first hard freeze of winter brings the most no-heat calls.
If your furnace will not light after these checks, call Mora Heating & Air and we will get it lighting safely.
Or tell us what your system is doing
Send us the details and we will call you back. If the house is very hot or very cold right now, calling is faster.