Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Appliance drained and discharged
Remove internal bypass from left hand side hydraulic block
Note.
By-pass is located behind the safety valve, take care when removing as the by-pass has a tendency to pop out

Observation:

Inspect the bypass valve for contamination and damage.
Ensure there is light spring tension to confirm correct operation.