Your furnace has one very important job: keep your home warm. So when it starts blowing cold air, making strange noises, or taking an unscheduled day off, you’re allowed to have questions.

The good news? Some furnace problems come down to something simple, like a thermostat setting or a dirty filter. Others need a trained technician to figure out what’s happening behind the scenes.

Here are five common furnace problems, the basic checks you can make at home, and when it’s time to give Harding Your Home Comfort Centre a call.

1. My Furnace Won’t Turn On

Your thermostat says heat. Your furnace apparently didn’t get the memo.

If nothing happens when you turn up the temperature, start with the basics:

• Check the thermostat: Make sure it’s set to HEAT and the temperature setting is above the current room temperature. Check whether a programmed schedule is overriding your adjustment.
• Check the batteries (if applicable): A blank screen or low-battery warning could explain the lack of response.
• Check the furnace power switch: It can look like a regular light switch and may have been accidentally turned off.
• Look at the electrical panel: A tripped furnace breaker needs attention. If you’re unsure why it tripped, or it trips again after being reset, leave it off and arrange professional help.

If the furnace still won’t start, contact Harding. Ignition, wiring, and internal component issues need a qualified technician—not a hopeful series of resets.

2. My Furnace Keeps Turning On and Off

A furnace should cycle on and off throughout the day. But if it keeps shutting down directly after starting, before your home reaches the temperature you’ve set, that’s called short cycling. Essentially, it’s cutting the heating cycle short instead of finishing the job.

Restricted airflow is one possible cause. A clogged filter can cause heat to build up inside the furnace, triggering a safety control to shut the burners down.

What you can check:

• Inspect the filter and replace it if dirty, using the size and type recommended for your system. Turn the furnace off before changing it and follow the owner’s manual.
• Make sure supply vents are open and return grilles aren’t blocked by furniture, rugs, or other household clutter.
• Notice whether direct sunlight or a nearby heat source could be affecting the thermostat’s temperature reading.

If the short cycling continues, book a service visit. Thermostat faults, equipment sizing, and internal furnace problems can also cause short cycles. Your furnace’s stop-and-start routine deserves a proper diagnosis.

3. My Furnace Is Making Strange Noises

A gentle hum or the sound of air moving is expected. A new soundtrack of banging, grinding, or squealing deserves attention.

Unusual noises can point to loose or worn components, including problems with the blower motor. The sound alone won’t tell you exactly what’s wrong, though, so resist the urge to diagnose it by volume.

What to do: Note when the sound happens—at startup, while running, or as the furnace shuts down—and share that with your technician. If you can safely record it, that may help too.

For loud banging, grinding, or other severe new noises, turn the furnace off and arrange service. Leave internal adjustments and repairs to a qualified professional.

4. My Furnace Runs, but My Home Still Feels Cold

You can hear it working, but the living room still has you reaching for another blanket.

If warm air is coming from the vents but your home isn’t reaching the thermostat setting, check how that air is getting around:

• Inspect the filter. Restricted airflow can reduce the amount of heated air reaching your rooms.
• Check vents and returns. Move anything blocking them, including that couch that fit perfectly everywhere except over the grille.
• Review the thermostat schedule. Make sure it hasn’t switched to a lower temperature setting.

If only certain rooms feel cold, mention that when you call. Air distribution, ductwork, or drafts may be contributing. If the whole house struggles to warm up, a technician can assess furnace performance and whether the system is meeting your home’s heating needs.

5. My Furnace Is Blowing Cold Air

An indoor breeze is lovely in July. During an Ottawa winter? Less charming.

A brief rush of cool air at the beginning of a heating cycle can happen while the air in the ducts warms up. Air that stays cold calls for a closer look.

Start with the thermostat: Confirm it’s set to HEAT. If the fan is set to ON, it can circulate unheated air between heating cycles. Selecting AUTO generally makes the fan run with the heating cycle instead.

Also check the filter. If restricted airflow causes overheating, a safety control may shut off the burners while the blower continues running to cool the equipment.

If these checks don’t resolve it, contact Harding. Many modern gas furnaces use electronic ignition rather than a standing pilot light, so the old advice to “just relight the pilot” won’t apply to every system. Ignition faults, flame-sensing issues, and safety-control problems require professional attention.

Let’s Get Your Home Comfortable Again

You don’t need to become a furnace expert to check a thermostat or spot a dirty filter. But if those basic checks don’t solve the problem, you don’t have to spend your evening playing furnace detective either.

The team at Harding Your Home Comfort Centre can investigate the issue, explain what they’ve found, and help you understand the next steps.

Contact Harding to arrange furnace service , and let’s get you back to enjoying a warm home.

Written by the Furnace Experts at Harding Your Home Comfort Centre

Our knowledgeable team helps Ottawa homeowners troubleshoot furnace problems and keep their homes comfortable. We draw on that experience to explain what common symptoms can mean, what you can check yourself, and when it’s time to call in a professional.