Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Mains Reset Switch OFF
Remove control box cover

Measurement:

On older models an F9 fault code is a generic fault and may be due to a variety of reasons. For these PCB's the model should be run from the start sequence for correct diagnosis.
Please choose which PCB type is fitted to the appliance.
IRIS PCB fitted - Fault find from start sequence
SYMS17.0 fitted - Use fault code