Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Isolate flow and return valves
Discharge appliance primary water
Disconnect electrical connector from diverter actuator
Remove hydraulic cover by releasing the locking pin and withdrawing
Gently ease out the by-pass valve

Observation:

Inspect by-pass valve for contamination and damage.
Ensure there is light spring tension to confirm correct operation.
Note:
The internal by-pass is fitted in the left hand side of the hydraulic section.