When your furnace won’t turn on, start with the easy stuff: the thermostat, the furnace switch, the breaker and the air filter. If none of those fixes it, a failed igniter or a dirty flame sensor could be the reason the heat never kicks in. These checks can give you a good idea of what’s going on, but repairs on a gas furnace need a qualified technician.
Furnaces are the main heating system in 46% of Canadian homes, according to Statistics Canada’s 2023 data. So when yours quits during an Ontario cold spell, even a small problem feels like a big one.
If you’d rather have someone take a look, call a company that offers furnace repair Toronto.
Check these things before troubleshooting
You don’t need to open the furnace for any of these.
- Check the thermostat. Set it to Heat and turn it up a few degrees above the room temperature.
- Check the thermostat display. If the screen is blank, put in new batteries (if it uses them).
- Check the furnace switch. It usually looks like a regular light switch near the furnace. Make sure it’s on.
- Check the breaker. If it tripped, reset it one time. If it trips again, call a technician.
- Check the air filter. If it’s clogged with dust, replace it.
- Look for a visible error code. Some furnaces have a small window. If yours does, write down the code and look it up in the manual.
Please don’t remove furnace panels or bypass any safety switches. And don’t keep resetting a furnace that keeps shutting itself down.
How a gas furnace starts
It helps to know the order of things. The thermostat tells the furnace it needs heat. The furnace starts its ignition sequence and lights the burners. Then a flame sensor checks that there’s actually a flame.
If any step fails, the furnace may stop and show an error code. That can help you narrow things down, but it can’t tell you the exact cause. Only a proper inspection can do that.
Could the thermostat be stopping the furnace?
Sometimes, yes. If the thermostat isn’t sending the call for heat, the furnace has no reason to start. Make sure it’s set to Heat, the temperature is high enough and the display is working.
Here’s one that confuses a lot of people. If the fan is set to On, it keeps moving air between heating cycles, and that air can feel cool even when the furnace is fine. If the burners are running and the air still feels cold, read more about furnaces blowing cold air.
If the thermostat is asking for heat and the furnace still does nothing, the problem is probably inside the furnace.
Could a faulty igniter keep the furnace from lighting?
The igniter heats up or makes a spark to light the gas burners. When it fails, the furnace may go through its start-up steps but never light the burners.
You might hear the furnace start up and then try again and again. A technician can test the igniter and the parts around it to find the cause. Igniters break easily, and the repair means working inside a gas appliance.
That’s a job for a furnace technician in Toronto. In Ontario, gas work should be done by properly certified technicians and registered contractors
Could a dirty flame sensor shut the furnace down?
The flame sensor’s job is to confirm that a burner has lit. If it can’t detect a flame, the furnace shuts off the gas to keep things safe.
A common sign is a burner that lights for a moment and then goes out. The furnace may try again a few times before it stops. A dirty flame sensor can add to furnace short cycling, though other faults can look the same.
Have a furnace technician in Toronto check the sensor and find the real cause. Don’t clean or adjust parts inside the furnace unless your manual says it’s a safe task for homeowners.
What does furnace safety lockout mean?
After several failed start-up attempts, some furnaces go into safety lockout. That means the furnace stops trying, either for a while or until it’s reset. The control board may show an error code that points to the problem.
Write down the code and check your furnace manual. Try not to keep switching the power off and on or resetting the furnace. If it keeps shutting down, it needs a proper diagnosis.
A technician may also put a red tag on a gas appliance if they find a safety issue. Follow the instructions on the tag, and don’t use the appliance until the problem is fixed. Learn more about a red tag.
When should you call a furnace professional?
Call for service if the furnace keeps failing to ignite, shuts down soon after starting, shows an error code, or trips the breaker again after one reset.
If you smell gas, leave the house and call your gas utility or emergency services from a safe place. If a carbon monoxide alarm sounds, or anyone has a headache, dizziness, nausea or confusion, get everyone outside and call 911. Ontario says to call 911 from outside if a CO alarm goes off or people may have CO poisoning.
If you need help figuring out the problem, book furnace repair Toronto.
What does a furnace service visit cost?
The price depends on the company, what they find and what needs to be repaired. Before anyone comes out, ask if the first fee covers diagnostic time and whether parts or repairs cost extra.
For more detail, see what a technician charges per visit.
Why won’t my furnace turn on when the thermostat is set correctly?
The thermostat may be fine. The furnace could have a power problem, a clogged filter, a failed igniter, a dirty flame sensor or another fault. Write down any error code, and book a professional inspection if the basic checks don’t fix it.
Can a dirty flame sensor stop a furnace from working?
Yes. If the sensor can’t detect a flame, the furnace may shut off the gas and stop heating. Other problems can cause the same symptoms, so a technician should confirm the cause.
Should I keep resetting a furnace that won’t start?
No. Resetting it over and over can hide a recurring problem without fixing it. Write down any error code and call a technician if the furnace shuts down again.
Can I replace a furnace igniter myself?
It’s not a good idea. Igniters are fragile, and you have to open the furnace to reach one. Let a qualified technician inspect the system and handle gas appliance repairs.
What should I do if my carbon monoxide alarm sounds?
Get everyone outside and call 911 from outside. Don’t go back in until emergency responders say it’s safe.
Get help with a furnace that won’t turn on
Check the thermostat, the power and the filter first. If the furnace still won’t start, or it lights and then shuts off, have a qualified technician diagnose it. Visit the HVAC TRUST homepage to get started.
