Lennox HVAC Error Code E33: How to Fix It — Ignition Lockout

Q: How do I reset my Lennox furnace after error code E33?

Turn off the power to the furnace at the breaker for 30 seconds, then turn it back on. The system will attempt to restart automatically. If the error returns, the underlying issue must be fixed.

Q: Can a dirty flame sensor cause Lennox error E33?

Yes, a dirty flame sensor is the most common cause of flame proving failure. Cleaning the sensor with sandpaper or steel wool often resolves the error.

Q: What does flame lockout mean on a Lennox furnace?

Flame lockout means the furnace has attempted ignition multiple times but failed to detect a stable flame. It locks out to prevent unburned gas from accumulating.

Q: How much does it cost to fix Lennox error E33?

DIY repair costs are minimal if it's just cleaning the sensor. Professional service fees range from $150 to $400, depending on the needed repair (e.g., replacing ignitor or gas valve).

Q: Is it safe to run my furnace with error E33?

No. The furnace locks out for safety. Attempting to bypass the lockout or continuously resetting can lead to gas buildup or a fire hazard. Fix the root cause first.

Abstract

Lennox error code E33 indicates an ignition lockout due to failed flame proving. This means the system attempted to ignite but did not detect a stable flame, causing a safety shutdown. This guide will help you troubleshoot and fix common causes, such as a dirty flame sensor, gas supply issues, or ignition problems.