Furnace Repair London Ontario Troubleshooting Common Issues

14 June 2026

A furnace that stumbles during a Grey County cold snap is a nuisance. A furnace that quits on a February night in London, Ontario can be a crisis. Our winters swing from damp shoulder seasons into deep freezes below minus 20 C with windchill. Equipment that seemed fine in November can show its weak points by January. After years of climbing in and out of basements and crawlspaces around Old South, Byron, and the north end, I’ve come to respect two truths. First, most furnace outages trace back to a handful of issues you can spot quickly. Second, a careful approach beats guesswork. If you start with safe checks and follow the clues, you’ll either get the heat back or you’ll have solid information when you call for furnace repair London Ontario pros.

This guide unpacks the most common problems, how to recognize them, what to do, and when to stop and bring in a licensed tech. It also covers decisions around repair versus furnace installation, because London’s housing stock ranges from pre-war homes with tight mechanical rooms to new builds with high-efficiency venting. The constraints are real, and they matter.
First, respect safety and the law
Natural gas furnaces are safe when installed and serviced correctly. They can be dangerous when they are not. Ontario’s Technical Standards and Safety Authority governs gas work, and it requires licensed G2 or G1 technicians for tasks that involve gas lines, burners, and heat exchangers. As a homeowner, you can check filters, thermostats, power, and vents. You shouldn’t be removing burner assemblies, altering gas pressures, or defeating a safety switch. If you smell gas, hear a hissing line, or a carbon monoxide alarm sounds, leave the building and call your gas utility and emergency services.

It helps to know what you are hearing and seeing. A modern furnace has several layers of safeties. If any one of them reports trouble, the control board may lock out. When that happens, the LED on the board will flash a code that points to the suspect. When I walk in, the first thing I do is read that code. It narrows the field fast.
How a modern gas furnace works in plain language
Knowing the sequence of operations makes troubleshooting much easier. When there is a call for heat, the control board checks the pressure switch to ensure the exhaust path is clear. The inducer fan starts, pulling air through the heat exchanger. The control looks for proof from the pressure switch. Then the igniter glows or sparks. The gas valve opens, the burners light, and the flame sensor confirms flame. After the heat exchanger warms, the main blower starts to move air through the ducts.

Any interruption in that chain stops the process. A split in a condensate line can stall the pressure switch. A dirty flame sensor can end the burn a few seconds after ignition. A fried blower capacitor can keep the blower from turning, which triggers a temperature limit switch. Each of these failures leaves a trail.
A rapid triage you can do before calling
Here is a concise homeowner checklist I use when talking to someone on the phone ahead of a service call. It often fixes the problem or at least gets us better data.
Confirm the thermostat is set to Heat, the setpoint is above room temperature by 2 to 3 C, and the batteries are fresh if it uses them. Check the furnace switch, breaker, and any GFCI outlet in the area. Make sure the furnace plug is fully seated and the service switch is on. Replace or remove a severely clogged filter. If you can’t see light through it, it’s overdue. For a quick test, run briefly with the filter out to see if the furnace completes a cycle. Inspect the intake and exhaust pipes outside. Clear frost, leaves, or nests. In a blizzard, vents along the side wall can bury in snow. Note any blinking LED code on the control board, and listen. Does the inducer start, does the igniter glow, do you get flame for a few seconds then shut down?
If the furnace fires once then cuts out, or it never lights at all, the details you observed will guide the next step. If it starts and then overheats, that tells a different story.
Thermostat and control miscommunication
Thermostats seldom fail outright, but when they do, the symptoms range from erratic cycles to a furnace that never gets the call. Smart thermostats complicate things with C-wire requirements and adaptive recovery logic. In London’s older homes, I often see two-conductor thermostat wire running to high-efficiency units that expect a common wire for stable power. The homeowner then adds a battery-powered smart stat and we get nuisance resets.

A plain test helps. Set the thermostat to Fan On. If the blower runs, the furnace has power and the fan circuit works. If it doesn’t, check the switch and breaker. With power confirmed, pull the thermostat off its base and inspect for corrosion or a loose wire. For systems that allow it, you can jumper R to W at the furnace control board temporarily to simulate a heat call. If the furnace runs reliably on a jumper but not through the thermostat, that points to the stat or wiring.

Be cautious with multi-stage equipment and heat pumps tied into a furnace. Miswiring O/B or W2 can create strange behaviour. If a smart stat was added recently and your problems started soon after, look there first. Heating and cooling London Ontario contractors see this pattern every fall when homeowners upgrade thermostats before the first real cold week.
Airflow restrictions and the chain reaction they cause
A furnace breathes. Restrict the return air and you get rising temperatures in the heat exchanger. The limit switch opens, the burners shut off, the blower runs to cool the heat exchanger, and then the cycle tries again. From the homeowner’s side it looks like short cycling or lukewarm air. I have pulled filters in some units that were packed with drywall dust from a recent renovation, or with pet hair after a new puppy arrived. A standard pleated filter in a typical 2,000 square foot home with regular traffic and pets should be replaced every 60 to 90 days. If renovations kick up dust, change it more often.

Duct issues also matter. Closed or crushed returns, furniture pressed against the return grill, or too many supply registers shut in unused rooms can starve airflow. In older houses near UWO with retrofitted ductwork, I sometimes find a return trunk that is undersized for a new high-efficiency furnace. The result is chronic high-limit trips. The fix can be as simple as opening more returns or as involved as adding a dedicated return to a basement suite.

Listen to the blower. If it hums but does not spin freely, you may have a weak capacitor or failing motor. A PSC blower motor that should draw 6 to 8 amps might pull higher when the capacitor fails. ECM motors show different symptoms, often with fault codes of their own. This is where DIY hits a limit. Testing and replacement needs the right meter and parts.
Ignition problems and the humble flame sensor
If the furnace seems to light, then shuts down within a few seconds and tries again, suspect a dirty flame rod. The flame sensor is a steel rod that sits directly in the burner flame. It measures microamps of current. A thin film of oxidation or silica from a dusty basement can break that signal. I keep a handful of 220 grit emery cloth pieces in my tool bag for exactly this. Lightly clean the rod, re-seat it, and many intermittent problems vanish. If you do this yourself, cut power first and be careful not to crack the ceramic insulator. Do not sand an igniter. Hot surface igniters are brittle and easily ruined by handling oils or abrasive cleaning.

Gas valves and ignition modules can fail, but look at simple causes first. Loose grounds, dirty burners, or misaligned igniter gaps are more common than a bad valve. When a tech says a control board is fried, they should be able to show you scorch marks, swollen capacitors, or diagnostic evidence, not just a shrug.
Condensate drains, pressure switches, and winter reality
High-efficiency furnaces pull heat so effectively that water condenses in the heat exchanger. That water must drain. A clogged trap or a sagging vinyl tube can fill with water and hold the pressure switch open. The furnace will either never light or it will shut down mid-cycle. In London’s older basements with long horizontal runs to a floor drain, I often find low spots that collect slime. The fix is to clear the line and support it so it slopes consistently. Rinse the trap. On units that vent out a side wall, the termination can frost up during a cold snap, which again leaves the pressure switch without the right differential. Keep those terminations clear by design, far enough off grade to furnace repair London https://emilianonazy401.timeforchangecounselling.com/top-rated-furnace-repair-london-ontario-trusted-local-technicians handle snow.

Anecdote from a January call in Masonville: a two-year-old furnace would run for five minutes, then quit. The code read pressure switch open. The condensate pump was fine, and the vent was clear outside. The problem was a kinked rubber hose at the inducer port, just enough to pool water. Straightened and clipped, the code went away and stayed away. Five-minute fix after an hour of hunting because the kink was behind a bundle of control wires.
Noises and smells that tell the story
Furnaces talk. A high-pitched whine at startup often points to the inducer bearings. A rumble after ignition can be delayed lighting due to dirty burners. Metallic rattles might be sheet metal expansion, which is harmless, or a cracked heat exchanger, which is not. If you smell raw gas for more than a second or two at light-off, shut it down and get a tech. If you smell a sweet solvent odor, you might be getting a whiff of antifreeze from a leaking coil on a dual-fuel setup, or you might be misattributing ozone from an electronic air cleaner. Track the source. Use a CO monitor in the utility area and on the bedroom level. They are inexpensive compared to the stakes.
Short cycling: different roots, same frustration
Short cycling wastes gas and wears components. Causes include oversized equipment, restricted airflow, a failing limit switch, a bad control board that misreads temperatures, or even a thermostat located over a supply register. I see the last one more than you’d think, especially in flipped homes where walls moved and the stat stayed on an interior column. The stat heats up quickly, ends the call early, and your main rooms never reach setpoint. Relocating a thermostat is not glamorous work, but it solves a lot of comfort complaints.

Oversizing is common after a furnace installation that did not include a heat loss calculation. The old unit might have been 120,000 BTU input to handle single-pane windows and no insulation in 1975. After a deep energy retrofit, the house might now need 50,000 to 70,000 BTU. If you drop in a 100,000 BTU furnace because that was what was in stock, it will satisfy small calls in minutes and shut off, repeat all day, and never hit steady state. If you are considering furnace installation London Ontario homeowners benefit from a proper Manual J style load calculation. It pays back in comfort, noise reduction, and reliability.
Frozen intake or exhaust during a cold snap
Sidewall vents are efficient, but they live in the weather. When the lake effect snow comes sideways off Lake Huron, intakes pack with powder. Moist exhaust can form icicles around the termination. The furnace loses its proof of draft and shuts down. Clearing vents is within a homeowner’s ability, but if it recurs, a termination kit or a different vent configuration might help. The vent must be installed to code, with separation between intake and exhaust, and at a height that accounts for snow load. I have seen vents tucked under decks where snow drifts and eddies right into the intake. A professional can rework that and save you midnight shovelling.
A careful reset if your furnace locks out
Control boards will often lock out after several failed ignition attempts. A power cycle clears it, but do this thoughtfully.
Turn the furnace power switch off and wait at least 60 seconds to let capacitors discharge. Set the thermostat to Off and Fan Auto to avoid immediate calls. Restore power, watch the control board for a normal idle code, then set the thermostat back to Heat. Observe the full start sequence. Listen for inducer, watch for igniter glow, confirm ignition, then blower. Note any step that fails or repeats. If the furnace fails again with the same behaviour, stop. Do not keep resetting. Record the fault code and call for service.
This approach protects the equipment and gives the technician a clean data point. Repeated resets can flood the burner with gas, stress igniters, or overheat components.
What repairs cost in our market
Numbers vary by brand and availability, but in London Ontario you can expect general ranges for common furnace repair items. Capacitors and simple switches usually land in the 150 to 300 CAD range installed. Hot surface igniters typically fall between 200 and 400 CAD depending on part and access. Flame sensors, if not simply cleaned, are similar. Condensate pumps and traps, 200 to 350 CAD. Pressure switches, 250 to 450 CAD. Control boards can range widely, often 450 to 900 CAD or more. ECM blower motors are the big ticket, commonly 800 to 1,600 CAD installed. These are ballpark figures based on typical service rates and parts availability I’ve seen across heating and cooling London Ontario shops. After-hours service adds a premium.

Be wary of any quote that leaps to heat exchanger replacement or a full system swap without a clear diagnosis. Heat exchangers do fail, and a cracked exchanger is not negotiable, but the tech should be able to show you a breach with a mirror or camera and explain the test. For older units with discontinued exchangers, a replacement furnace may indeed be the only safe path.
When repair flips to replacement
There is a rough rule in our trade: if a repair exceeds 30 percent of the cost of a new furnace and the unit is more than 12 to 15 years old, consider replacement. The context matters. A 12-year-old mid-efficiency furnace with a failed control board might be worth repairing if the heat exchanger is sound and the venting is aluminum B-vent in good shape. A 20-year-old unit with a seized blower and corroded burners is a different story.

When you plan a furnace installation, look beyond the sticker. Consider:
Heat load and sizing based on your home’s insulation, windows, and air leakage, not just square footage. Duct condition and static pressure. A high-efficiency furnace will underperform if the ductwork is too restrictive. Venting path. Sidewall terminations need clear space from grade and openings. Roof vents require safe routing and support. Combustion air in tight homes. Energy retrofits often tighten the envelope. The furnace may need dedicated makeup air. Integration with AC or heat pump. If you plan to add or upgrade cooling, select a blower that matches both seasons.
I have had good results pairing variable-speed furnaces with two-stage gas valves in homes that struggle with temperature swings. The furnace runs longer at low fire, evens out the rooms, and improves humidity control. It costs more up front than a single-stage unit but pays back in comfort. For homeowners eyeing a hybrid setup, London’s shoulder seasons are perfect for a cold-climate heat pump with the furnace as backup below, say, minus 10 C to minus 15 C. That said, duct design and electrical capacity set the boundaries. Don’t let the promise of savings outrun your house’s realities.
Maintenance that actually prevents calls
Annual maintenance is not a ritual, it is risk reduction. A proper tune-up on a high-efficiency gas furnace includes cleaning and testing the flame sensor, checking igniter resistance, inspecting burners, verifying manifold gas pressure, confirming temperature rise within the rated range, measuring static pressure, checking the condensate trap and hoses, and confirming proper venting and termination. On ECM blowers, I check for fault history and motor module health. On older PSC motors, I test the capacitor. I also look at the filter rack and seals. A bypass around the filter lets dust load the blower and coil, which slowly strangles airflow.

If your furnace sits near the laundry, keep lint under control. If you recently finished a basement, seal off returns during sanding and clean ducts afterward. I still remember a Kilworth home where the homeowner replaced three flame sensors in a year. The root cause was a new workshop next to the furnace. Every time he sanded a project, dust drifted to the burners. A simple curtain and a better return filter ended the streak.
Local quirks worth noting
London gets wet autumns and spring thaws that flood older basements. Furnaces installed on the floor in a shallow depression become sitting ducks for minor water events. Elevate the unit on a proper stand. Sump pumps fail at the worst times, so condensate pumps that discharge into a floor drain tied to a sump can surprise you. Better to run condensate to a sanitary drain when code and layout allow it.

Critters love warmth. I have pulled bird nests from terminations in Old East Village and found a mouse wedged in a pressure tube in a rural property just outside city limits. Screen terminations correctly, and route small tubing so it rises in a gentle loop rather than lying flat where dust and debris accumulate.

We also see electrical peculiarities in older homes. Shared neutrals, bootleg grounds, or loose splices in a junction box can make a smart thermostat misbehave and a furnace board reset randomly. If lights dim noticeably when the furnace starts, have the electrical service checked. ESA licensed electricians in the region can sort that out before it becomes a furnace scapegoat.
What to expect from a professional visit
A good technician won’t just swap parts. They will verify the complaint, observe a full cycle, pull and interpret error codes, and test components rather than guessing. You should hear numbers. Manifold gas pressure in inches water column. Temperature rise in degrees across the heat exchanger. Static pressure in inches water column across the blower. Microamp signal at the flame sensor. These figures separate true diagnosis from part darts.

If the recommendation is furnace repair, you’ll get a clear scope and parts identified by name and model. If the recommendation is replacement, the contractor should discuss sizing, venting, ductwork, and controls. For a furnace installation London Ontario homeowners deserve bids that explain why a particular model fits the house, not just a brand logo and a bottom line.
When you need help fast
Heating and cooling London Ontario companies get swamped on the first deep cold spell. If your furnace dies in that window, triage appointments fill. Calling with a clear description of symptoms and any error code helps schedulers prioritize. If you can safely perform the quick checks above and report what you found, you stand a better chance of being slotted correctly. Many shops hold emergency spots for no-heat calls involving seniors, small children, or medical needs. Say so if that applies.

Portable space heaters can keep a room habitable for a night, but use them on dedicated outlets, keep clearances, and never sleep with an unvented fuel heater running. If pipes are at risk of freezing, run taps at a trickle and open cabinet doors to let room air reach plumbing along exterior walls. These are stopgaps, not solutions.
Final thoughts from the basement floor
The best furnace is the one you forget about because it just runs. Getting there is rarely about gadgets and more about fundamentals. Clean air in, clean venting out, correct fuel, intact safeties, and ducts that match the blower. Most no-heat calls I’ve handled across the city reduce to a half dozen culprits. When you know what to look for, you fix them fast or you call for furnace repair with confidence and specifics.

And if your unit is at retirement age, approach replacement with the same discipline. Size it right, vent it properly, ensure your ducts and controls are up to the task, and choose a contractor who measures instead of guessing. Do that, and the next polar vortex will be a non-event inside your walls, exactly how it should be.

<h2>Hometown Heating and Cooling — Business Info (NAP)</h2>

Name: Hometown Heating and Cooling

Website: https://www.hometownhc.ca/ 
Email: sales@hometownhc.ca 
Phone: (519) 425-0555

Service Area: London, Woodstock, and Ingersoll (Southwestern Ontario)

<h3>Ingersoll Location</h3>
Address: 113 Mutual St N, Ingersoll, ON N5C 1Z8 
Map/listing URL: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.042608,-80.8860254,17z/data=!3m1!4b1!4m6!3m5!1s0x882e9bfee0d53bf3:0x9f78b1810f24ad23!8m2!3d43.0426041!4d-80.8834505!16s%2Fg%2F1tdgqgkq 
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<h3>London Location</h3>
Address: 45 Pacific Ct Unit #11, London, ON N5V 3N4 
Map/listing URL: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.0088901,-81.1800363,17z/data=!4m6!3m5!1s0x882c1f2183b77adf:0x7511cc8383025dcb!8m2!3d43.0101465!4d-81.1752898!16s%2Fg%2F11fsm535_n 
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Hours: Monday-Friday: 8:00AM-5:00PM Saturday & Sunday: Closed

Open-location code (Plus Code): 2R6F+3V London, Ontario

Socials (canonical https URLs): 
Facebook: https://www.facebook.com/Hometownhandc 
Instagram: https://www.instagram.com/hometownhandc/ 
LinkedIn: https://www.linkedin.com/company/hometownhc/

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https://www.hometownhc.ca/

Hometown Heating and Cooling provides residential HVAC services across London, Woodstock, and Ingersoll in Southwestern Ontario. 
Services include heating and cooling installation and repair, fireplace services, duct cleaning, ductless mini-splits, and gas line work (service scope varies by job). 
The Ingersoll location is listed at 113 Mutual St N, Ingersoll, ON N5C 1Z8. 
The London location is listed at 45 Pacific Ct Unit #11, London, ON N5V 3N4. 
To contact Hometown Heating and Cooling, call (519) 425-0555 or email sales@hometownhc.ca. 
For directions, use the listings: https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.042608,-80.8860254,17z/data=!3m1!4b1!4m6!3m5!1s0x882e9bfee0d53bf3:0x9f78b1810f24ad23!8m2!3d43.0426041!4d-80.8834505!16s%2Fg%2F1tdgqgkq and https://www.google.com/maps/place/Hometown+Heating+and+Cooling/@43.0088901,-81.1800363,17z/data=!4m6!3m5!1s0x882c1f2183b77adf:0x7511cc8383025dcb!8m2!3d43.0101465!4d-81.1752898!16s%2Fg%2F11fsm535_n

<h2>Popular Questions About Hometown Heating and Cooling</h2>

What areas does Hometown Heating and Cooling serve? 
Hometown Heating and Cooling serves Southwestern Ontario, including London, Woodstock, and Ingersoll.

What services does Hometown Heating and Cooling provide? 
Services listed include heating and air conditioning work, fireplaces, duct cleaning, ductless mini-splits, and gas line services (availability varies).

Where are Hometown Heating and Cooling locations? 
Ingersoll: 113 Mutual St N, Ingersoll, ON N5C 1Z8. 
London: 45 Pacific Ct Unit #11, London, ON N5V 3N4.

Do they offer emergency service? 
The website indicates 24/7 emergency service for urgent HVAC situations.

How can I contact Hometown Heating and Cooling? 
Phone: +1-519-425-0555 tel:+15194250555 
Email: sales@hometownhc.ca mailto:sales@hometownhc.ca 
Website: https://www.hometownhc.ca/ 
Facebook: https://www.facebook.com/Hometownhandc 
Instagram: https://www.instagram.com/hometownhandc/ 
LinkedIn: https://www.linkedin.com/company/hometownhc/

<h2>Landmarks Near London, Woodstock, and Ingersoll</h2>

1) Victoria Park (London) https://www.google.com/maps/search/?api=1&query=Victoria%20Park%20London%20Ontario 
2) Fanshawe College (London) https://www.google.com/maps/search/?api=1&query=Fanshawe%20College%20London%20Ontario 
3) Pittock Conservation Area (Woodstock) https://www.google.com/maps/search/?api=1&query=Pittock%20Conservation%20Area%20Woodstock%20Ontario 
4) Woodstock Art Gallery https://www.google.com/maps/search/?api=1&query=Woodstock%20Art%20Gallery%20Woodstock%20Ontario 
5) Ingersoll Cheese & Agricultural Museum https://www.google.com/maps/search/?api=1&query=Ingersoll%20Cheese%20%26%20Agricultural%20Museum%20Ingersoll%20Ontario 
6) Harris Park (London) https://www.google.com/maps/search/?api=1&query=Harris%20Park%20London%20Ontario