Ignitors & Ignition Switches

Signs include:

• No glow during startup; furnace clicking but doesn’t ignite.
• Furnace blows cold air or cycles on/off repeatedly.
• Circuit breaker trips during ignition attempt.
• Physical damage like cracks or white spots on the ignitor.

1. Ensure power is off and ignitor cooled.
2. Visually inspect for cracks or discoloration.
3. Use a multimeter on the lowest ohms setting:

• Ideal resistance is typically 40–100 Ω (some sources say 50–400 Ω). Values outside that range indicate a faulty ignitor.

1. Turn off power and gas.
   Access the ignitor—usually located near the burners.
2. Unplug its connector and carefully remove it; surface is extremely brittle—handle with care and never touch the ceramic.
3. Insert the replacement (same spec) and reconnect.
4. Restore power/gas, then test operation.

• Thermal stress from heating/cooling cycles leading to cracks.
• Debris or dust buildup can cause damage or short circuits.
• Voltage irregularities like power surges.
• Physical impact or contaminants—for example, oils from skin.

• Silicon nitride ignitors: typically 7–15 years.
• Silicon carbide ignitors: about 3–5 years due to brittleness.
• Modern units often list a lifespan of around 7 years.

They draw a few amperes momentarily during startup. If it draws too high or low current, the ignitor may fail or trip the breaker. Reddit techs advise comparing current draw against manufacturer specs; significant deviations mean replacement.

• Immediately if it shows visual damage or fails the multimeter or current test.
• As a preventive measure around the end of its typical lifespan: ~5 years for SiC, ~10 years for SiN.
• Consider replacement during routine maintenance to avoid mid-winter breakdowns.