F codes are blocking faults, A codes are fault codes, however A or F may be displayed in front of any number, it is the number that is most relevant and the tests followed will be the same for each.

Measurement:

Please select from the appropriate fault code below:
F07 Flue gas temperature is too high
F08 CH flow over temperature condition
F09 CH return over temperature condition
F10 No 1 flow temperature sensor error
F11 Return temperature sensor error
F12 DHW sensor error
F13 Flue gas temperature sensor error
F14 No 2 flow temperature sensor error
F15 Incorrect frequency feedback from fan
F17 Harness or wiring fault
F21 Close to high pressure limit 2.5 - 2.8