F01 Flue temperature switch / low water

What the control is telling you

Flue temperature limit switch tripped or, if the optional UL353 LWCO is fitted, water level is low. Lockout with 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

• Low water level (UL353 LWCO installed)
• Flue obstructed or overheated
• Flue temperature switch failed
• Cracked target wall in the combustion chamber

Test and repair steps

1. With an LWCO check for the red LED on its control box, correct the low water condition, press the LWCO reset (LED turns green) then reset the boiler at the display
2. Check the flue for blockage or heat damage and repair
3. Push the red reset button on the flue temperature switch (inside the rear access door); the switch must be below 90 F to reset
4. Press RESET on the display, run the boiler and compare an external flue thermometer to the FLUE reading
5. If the flue temperature is in spec and the switch trips again, replace the switch
6. If the flue is hot, check combustion; inspect the target wall and replace if cracked

Models that show this code

12 models in Elite EL

Other codes on the same units

• E03 System sensor failure (cascade)
• E07 Flue temperature high
• E19 Line voltage frequency out of range
• F00 Water high temperature (ECO)
• F02 Supply sensor failure
• F03 Return sensor failure
• F04 Flue sensor failure
• F05 Supply temperature high