Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove vent plug from the pump or loosen as required
Note:
Water may exist from the pump vent when the plug is removed, care should be taken this does not run on to the electrics, water should be captured in a small container.

Observation:

Insert small slotted screwdriver into the vent and engage pump shaft or engage pump shaft with vent plug (depending on type) spin the shaft.
Does the pump spin freely?
Replace and tighten vent plug after test.