Set Appliance State:

Mains Power Off
CH Demand
Purge Switch in NORMAL position
HW Switch in OFF position
CH Switch in CH Continuous position
CH Potentiometer set to maximum
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the Boiler to operate with CH demand.
Remove the demand, does the CH Pump overrun for a period of 10 minutes?