Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On

Observation:

With water flowing from a hot water tap, isolate the cold feed isolation valve to the boiler.
Does the flow from the hot water tap cease? (see note)
Note.
It may take a while for the flow to cease, as there will be some water left in the pipework, however the remaining water should not be under pressure.