Display shows E04, furnace may lock out after detecting abnormal flame signal

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Shorted ionization probe to ground, Moisture on flame sensor, Control board flame circuit fault, Electrical noise or incorrect grounding

Safety: Turn off power and gas.

Inspect ionization probe: Ensure the probe is not touching the burner or other metal parts except at the tip. Check the ceramic insulator for cracks and replace if damaged.
Dry moisture: If there is condensation or water around the burner or sensor, dry the area thoroughly and correct any condensate leaks.
Check grounding and neutral: Verify correct polarity and grounding at the mains connection. Incorrect wiring can cause false flame signals.

If E04 continues, the control board may require replacement.

Hard 4/5

Ionization Probe

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