F04 Flue sensor failure

What the control is telling you

Flue temperature sensor has failed. Lockout, pump on. Control: FAULT light red steady and LOCKOUT shown on lower line; reset with RESET held over 1 second after repair.

Applies to: EL-80, EL-110, EL-150, EL-220, EL-299, EL-399 (N/LP)

Likely causes

• Sensor damaged or corroded
• Wiring connection fault

Test and repair steps

1. Inspect the flue sensor for damage or corrosion; replace if needed
2. Check and repair the electrical connection
3. Measure the sensor resistance and compare with the chart; it should match the flue temperature, otherwise replace the sensor

Models that show this code

12 models in Elite EL

Other codes on the same units

• F00 Water high temperature (ECO)
• F01 Flue temperature switch / low water
• F02 Supply sensor failure
• F03 Return sensor failure
• F05 Supply temperature high
• F06 Return temperature high
• F09 No flame on ignition
• F10 Flame loss