This display indicates that the return temperature sensor of the boiler has failed. This code indicates a serious safety issue and the boiler will not restart until the sensor is replaced by a technician and he pushes the RESET button 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.
- Check circulator pump operation.
- Assure that there is adequate flow through the boiler by accessing the status menu and assuring that there is less than a 50°F rise from the return thermistor to the supply thermistor.
- Troubleshoot thermistor by following steps in F02.
