Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch to Water
Disconnect the wires to the DHW Diverter Valve solenoid
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to ignite and run.
With a flow rate at the tap of approximately 12 l/min is there a temperature rise of approximately 40°C?