No Heat? Furnace Checks for Durham Region
Durham Region winters don’t ease you in. When temperatures drop below -10°C and your furnace stops producing heat, you need answers fast — not a generic troubleshooting article written for someone in a warmer climate.
This guide covers what to check when your furnace isn’t working, what the warning signs are that you should stop and call a technician, and what to expect when we come out for a no-heat call. It applies to both older 80% AFUE systems — which are still common in Oshawa, Whitby, and the older parts of Durham Region — and the high-efficiency systems installed in newer homes across Bowmanville, Courtice, and Pickering.
If anything smells off, if your CO alarm has sounded, or if your furnace is making noises it hasn’t made before, skip this article and call us directly at (705) 344-3124.
Start here: the basics before anything else
Before assuming your furnace has failed, check these three things. They sound obvious, but they account for a surprising number of no-heat calls.
Thermostat settings: Make sure it’s set to Heat, not Cool or Fan Only, and that the setpoint is above your current room temperature. Check the batteries if your thermostat is battery-powered. A dead thermostat battery is one of the most common reasons a furnace won’t start, and it’s a five-minute fix.
The furnace power switch: There’s a wall switch near the furnace that looks identical to a standard light switch. It controls power to the unit. If it’s been accidentally switched off, which happens more often than you’d think, especially in utility rooms that double as storage, the furnace won’t respond to the thermostat at all.
The circuit breaker: Go to your electrical panel and find the breaker labelled for the furnace or HVAC. If it’s tripped to the middle position, reset it once by switching it fully off and then back on. If it trips again immediately, stop. A breaker that won’t stay on is telling you something is wrong electrically — repeated resets won’t fix it and can cause damage. Call us.
Check the furnace itself
If the basics are all fine, the furnace itself needs a closer look. Here’s what you can safely assess without any tools or technical knowledge.
The diagnostic light: Most furnaces made in the last 20 years have a small LED on the control board that blinks a code when something is wrong. There’s usually a legend on the inside of the furnace door that tells you what each flash pattern means. For example, three flashes might indicate a pressure switch fault, while two flashes might indicate an ignition failure. Note the pattern and have it ready when you call us. It significantly speeds up the diagnosis.
The furnace filter: A severely clogged filter can cause a furnace to overheat and shut down on the high-limit safety switch, which means the furnace technically works, but keeps shutting itself off before the house reaches temperature. Pull the filter out and hold it up to the light. If you can’t see through it, replace it. Standard 1-inch filters in Durham Region homes should be changed every 1-3 months during heating season, more frequently if you have pets.
The condensate drain (high-efficiency systems only): If you have a high-efficiency furnace, identifiable by the white PVC pipes going through the wall rather than a metal flue going up through the roof, it produces condensate water as part of the heating process. That water drains through a small plastic hose and pump. In winter, the drain line can freeze if it runs through a cold area of the basement, or the condensate pump can fail. If you see water pooling around the base of the furnace, or the drain line appears frozen, this is likely your issue. Don’t try to thaw it with an open flame – call us.
The intake and exhaust pipes (high-efficiency systems only): Your high-efficiency furnace pulls combustion air from outside through one PVC pipe and exhausts through another. Both terminate on an exterior wall, usually low to the ground. After a heavy snowfall or ice storm (both common across Durham Region from December through March) these pipes can become partially or fully blocked. Go outside and check that both pipe openings are clear of snow, ice, and debris. Clearing a blocked pipe has restored heat for many homeowners without any service call at all.
The blower door: The access panel on the front of the furnace has a small safety switch that prevents the furnace from running when the panel is open or not fully seated. Make sure it’s closed firmly and latched properly.
What the furnace is trying to tell you
A furnace that’s struggling before it fails will usually give you signals. In Durham Region, where heating season runs from October through April and temperatures regularly drop to -15°C or colder overnight, catching these early can be the difference between a repair and an emergency replacement.
Short cycling: The furnace turning on, running briefly, then shutting off before the house reaches temperatur, almost always indicates one of three things: a clogged filter causing overheating, a faulty flame sensor that can’t confirm the burner is lit, or a heat exchanger issue. The first you can fix yourself. The second is a relatively inexpensive repair. The third is serious and needs professional assessment immediately.
Delayed ignition: A loud bang or boom when the furnace starts happens when gas builds up in the combustion chamber before igniting. It’s hard on the heat exchanger and gets worse over time. If your furnace has been banging on startup, it needs a technician.
Weak heat output: The furnace runs continuously but the house never gets warm can point to airflow problems (ductwork, dampers, a blower issue) or a heat exchanger problem. In older homes in Oshawa and Whitby with original ductwork, it’s often a combination of duct leakage and an undersized system struggling on the coldest days.
Unusual smells: A faint dusty smell when the furnace first starts each heating season is normal. It’s dust burning off the heat exchanger. Any other smell warrants attention. A sulphur or rotten egg smell means gas. Turn the furnace off, leave the house, and call your gas utility before calling us. A burning plastic or electrical smell means something is overheating. A musty or mouldy smell coming from the vents can indicate an issue in the ductwork or air handler.
When to stop checking and call immediately
Some situations require a technician, not a homeowner troubleshooting guide. Stop and call us if:
- Your carbon monoxide detector has gone off. Evacuate first, call 911, then us.
- You smell gas anywhere near the furnace or in the house.
- The furnace is making grinding, scraping, or loud rattling sounds it hasn’t made before.
- The breaker trips more than once.
- You see scorch marks, melted components, or anything that looks burned around the furnace.
- The furnace ran fine yesterday and today produces no heat at all with no obvious explanation.
That last point matters more than people realize. A furnace that fails suddenly without warning (no gradual decline, no strange noises, no smells) has often had a component failure that a technician needs to diagnose properly. Attempting to reset or restart it repeatedly can sometimes make the diagnosis harder.
What to expect on a no-heat service call
When we come out for a no-heat call in Durham Region, here’s how it typically goes.
We start by getting the history from you: when it stopped, what you noticed, whether there have been any recent changes to the system or the house. The diagnostic light code is useful here if you noted it. We then run through a systematic check of the ignition system, gas valve, pressure switches, heat exchanger, blower, and controls.
For most common failures (ignitors, flame sensors, pressure switches, control boards) we carry the most frequently needed parts and can often complete the repair on the same visit. For less common parts, we’ll give you a clear timeline and keep the house as warm as possible in the interim.
If the repair cost is significant and the system is older, we’ll give you an honest assessment of whether repair or replacement makes more sense for your situation. Durham Region homes have a wide range of furnace ages (we service systems from a few years old to well over 20) and the right answer depends on the specific system, not a general rule. We prioritize no-heat calls during heating season and aim to get to you the same day wherever possible.
Furnace repair and replacement in Durham Region
We service and repair all major furnace brands across Durham Region including Oshawa, Whitby, Ajax, Pickering, Bowmanville, and Port Perry. For no-heat emergencies, call us directly at (705) 344-3124 — calling is faster than the quote form when heat is the issue.
If your furnace is older and this repair is one of several in recent years, it may be worth a conversation about replacement. We install high-efficiency gas furnaces and can also discuss hybrid systems that pair a furnace with a heat pump for improved efficiency and lower operating costs.
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HVAC Zack provides honest assessments of furnaces across Durham Region.
About The Author
Zack Laundrie is a licensed and insured HVAC technician with over 15 years of hands-on experience serving Durham Region homeowners. He specializes in heat pump installation, hybrid systems, and honest diagnostics across Oshawa, Whitby, Ajax, Pickering, Bowmanville, and Port Perry.