Furnace Flame Sensor Symptoms in Greater Vancouver

The flame sensor is a small but critical safety component in modern furnaces. When it fails or becomes coated with residue, it causes the furnace to shut down the gas valve within seconds of lighting — a very recognizable symptom pattern.

What This Symptom Means

The flame sensor generates a tiny electrical current when it detects the presence of a flame. If the furnace control board does not see this signal within a few seconds of ignition, it shuts off the gas valve as a safety measure. A dirty or failed sensor sends no signal even when the flame is present, causing a false shutdown.

Common Causes

• Oxidation or residue coating on the sensor rod reducing electrical conduction
• Sensor cracked or broken
• Control board not reading sensor signal correctly
• Grounding issue at sensor mount
• Sensor wire damaged or disconnected

What Homeowners Can Check Safely

• Look at the furnace status light — most furnaces blink a code for flame sensor failure (commonly 3 or 4 blinks — check your model label)
• Count the blink pattern and compare to the legend on the inside of the furnace door panel

When to Call a Licensed Technician

Some furnace issues require a licensed HVAC technician. Do not attempt to open gas lines, replace internal components, or reset persistent lockouts without professional diagnosis.

• Flame sensor cleaning with fine steel wool or emery cloth — a standard maintenance task
• Sensor electrical resistance testing with a multimeter
• Sensor replacement if cleaning does not resolve the fault
• Control board inspection if sensor tests good but fault persists

Frequently Asked Questions

Can I clean the flame sensor myself?

Some handy homeowners clean the flame sensor themselves, but it requires safely accessing the furnace interior, identifying the correct component, and knowing how to handle it without causing damage. A technician can clean and test it in under 30 minutes during a maintenance visit. If you are unsure, professional service is the safer choice.

How often does a flame sensor need to be cleaned?

Flame sensors typically need cleaning every 1–3 years depending on burn hours and fuel quality. Annual furnace maintenance usually includes this step. If your furnace is shutting off shortly after lighting, this is often the first component a technician checks.

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