Furnace Lights Then Shuts Off – Flame Sensor Issues After Winter Storm

After a winter storm, many homeowners across North America report the same furnace problem: the furnace lights, then shuts off within a few seconds. This issue often appears after power outages, extreme cold, or moisture exposure and is commonly caused by a faulty or dirty furnace flame sensor.

If your furnace was working before the storm but now won’t stay on, the flame sensor should be one of the first parts to check.

Why Winter Storms Cause Flame Sensor Problems

Winter storms create harsh conditions for furnace components, including:

• Power outages and sudden restarts

• High humidity and condensation inside the furnace cabinet

• Extreme cold affecting metal sensor surfaces

These factors can cause the flame sensor to become dirty, corroded, or electrically damaged, preventing it from properly detecting the burner flame.

Common Symptoms of Flame Sensor Issues

If your furnace lights and then shuts off shortly after ignition, you may notice:

• Burners ignite briefly, then turn off

• Furnace cycles repeatedly without producing heat

• Blower fan runs, but no warm air

• Furnace enters safety lockout mode

These symptoms often appear immediately after a winter storm or power restoration.

How the Flame Sensor Works (And Why the Furnace Shuts Off)

The flame sensor is a safety device that confirms the burner flame is present. If the control board does not receive a proper signal from the flame sensor within a few seconds, it shuts off the gas valve to prevent unsafe operation.

A weak or failed flame sensor will cause the furnace to shut down even though ignition occurs normally.

Quick Checks for Flame Sensor Problems

Before replacing parts, try the following:

1. Turn off power to the furnace

2. Inspect the flame sensor for dirt or discoloration

3. Clean the sensor gently with fine sandpaper or steel wool

4. Restore power and test the furnace

If the furnace still lights and shuts off, the flame sensor may need replacement.

When to Replace the Furnace Flame Sensor

You should replace the flame sensor if:

• Cleaning does not resolve the issue

• The furnace continues short-cycling

• The sensor shows corrosion or damage

• The furnace locks out after multiple ignition attempts

Flame sensors are inexpensive but critical for safe furnace operation.

Preventing Flame Sensor Issues After Future Winter Storms

• Schedule furnace maintenance before winter

• Keep the furnace cabinet dry and sealed

• Avoid repeated power cycling during outages

• Replace worn flame sensors proactively

Final Thoughts

If your furnace lights then shuts off after a winter storm, a flame sensor issue is one of the most common and easily fixed causes. Replacing a failed furnace flame sensor can quickly restore heat and prevent repeated shutdowns during freezing weather.

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