Set Appliance State:

On/Off Switch OFF
Isolate Mains Power to appliance as per TOPs P4
Ensure DHW demand is satisfied
Close the isolation valve on the integral bypass
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Appliance On/Off switch On.
Reset lockout as necessary.
Allow boiler to fire.
Does the circulation to the system improve?
After test open isolation valve on the bypass.