F01 indicates that the flue temperature limit switch of the boiler has tripped or that the water level in the boiler is low (this will only occur if the optional UL353 LWCO is installed). This code indicates a serious safety issue. The boiler will not restart until the flue cools down sufficiently or the water level is restored. A technician must repair the cause of the problem and push the RESET button first on the low water cut-off control box, then on the display. This situation is indicated by the red light on the display and the word LOCKOUT flashing on the display. During this lockout fault, the pump will be on as indicated on the second line of the display.
- If the boiler has a UL353 LWCO, check if the red LED on the LWCO control box is illuminated. If so, correct the low water condition and press the reset button on the LWCO control box to reset the LWCO. The LED should change to green. Press the reset button on the front panel of the boiler to reset the boiler control.
- Check the flue for obstructions or any sign of damage, especially signs of excessive heat. Repair as necessary. Push the red reset button on the flue temperature switch located on the flue inside the rear access door of the boiler.
NOTE: The switch temperature must be less than 90°F to reset. Press the reset button on the display. Run the boiler and check the flue temperature by using both an external thermometer in the flue pipe and the flue temperature display in the status screens. If the flue temperature is within specs and the switch trips, replace the switch. If the flue temperature is excessive, check and adjust combustion controls on the boiler. If the problem persists, inspect the target wall in the combustion chamber and replace it if cracked or damaged.
