My gas fireplace pilot light won't stay lit in cold Ottawa weather — what's causing this?

A gas fireplace pilot light that won't stay lit in Ottawa's extreme cold is almost always caused by one of three issues: a thermocouple failure, insufficient gas pressure during temperature drops, or a draft problem created by the freeze-thaw cycle affecting your chimney or venting system. This is particularly common in mid-to-late winter when Ottawa temperatures plummet to -25 or colder and barometric pressure changes become more extreme.

Why Cold Weather Triggers Pilot Light Problems

Ottawa's winter climate creates unique stresses on gas fireplace systems. The thermocouple — a small sensor that sits in the pilot flame and tells the gas valve that the pilot is lit — becomes less responsive in extreme cold. The sensor's electrical conductivity decreases slightly as temperature drops, which can cause the safety valve to cut gas flow to the pilot before it should. Additionally, when outdoor temperatures reach -20 degrees Celsius or lower, the pressure differential between inside and outside your home increases dramatically. If your gas fireplace uses a direct-vent system, the cold air flowing back through the vent pipe can cool the thermocouple enough to trigger a shutdown. If you have a B-vent system, the extreme cold temperature gradient can create downdraft conditions that extinguish the pilot or prevent it from igniting reliably.

The third culprit is freeze-thaw damage to the chimney or vent pipe itself. If your chimney has a cracked crown, damaged flashing, or spalling mortar, water enters the structure. When temperatures drop below zero — which happens 50 or more times per Ottawa winter — that water freezes and expands, potentially shifting the chimney slightly or creating ice blockages inside the vent pipe. Even a small obstruction or shift can disrupt the precise airflow that gas fireplaces require.

Do not attempt to troubleshoot gas fireplace problems yourself beyond basic observation. Gas work requires a TSSA-licensed gas fitter. Carbon monoxide is invisible and deadly, and improper diagnosis can create serious safety hazards. Your homeowner's insurance may not cover damage or injury from unlicensed gas work.

The most likely cause is thermocouple failure or a gas pressure issue, both of which require professional diagnosis. A TSSA-licensed gas fitter will test the thermocouple resistance, measure gas pressure at the appliance (which should match the manufacturer's specifications), check for air leaks in the combustion chamber that might allow cold drafts to reach the pilot, inspect the vent pipe for ice or blockages, and test carbon monoxide levels to ensure the appliance is operating safely. If the thermocouple needs replacement, the cost is typically $150 to $250 including labour. If the problem is gas pressure, it may involve adjustments at the meter or regulator, or issues with your gas supplier during extreme cold snaps (which occasionally happens in Ottawa during the deepest winter days).

If your chimney shows signs of deterioration — crumbling mortar, visible cracks in the crown, or spalling on the brick — that may be contributing to the problem. Ottawa's freeze-thaw cycle is relentless on masonry chimneys, and even minor damage can worsen dramatically during a single cold snap. A WETT-certified chimney inspector can examine the entire structure and vent path for damage that might be affecting performance.

Important warning: If the pilot light won't stay lit and you also notice any smell of gas, carbon monoxide detector alerts, or yellow/orange flames (instead of blue), stop using the fireplace immediately, open windows to ventilate the space, and call your gas fitter urgently. These are signs of a serious safety issue.

Timing matters in Ottawa — many homeowners discover pilot light problems in December or January when the deep cold hits. If you can schedule service in November or early December, before the coldest stretch of winter, you'll avoid a long wait. A licensed gas fitter can perform a full inspection, test, and any necessary repairs within a couple of hours.

When you're ready to have this diagnosed and repaired, a TSSA-licensed gas fitter is your essential next step. You can browse fireplace and gas service contractors through the Ottawa Construction Network directory at justynrookcontracting.com/directory to find licensed professionals in your area.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Luxe Painting and Renovations
• JC Carpentry
• Ottawa Masonry Contractor
• Dtech Services and Solutions Inc
• Geerts Roofing Inc