Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove wires from top two terminals of
connector X106 and make safe
Fit a wire link between top two terminals of
connector X106 as shown below
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance.
(press and hold the power button for 4 seconds then release)
Has the fault code now cleared?
Note:
If fault code clears with link fitted DO NOT leave link in place rectify issue with underfloor heating controls.