Set Appliance State:

Mains Power Off
Rotary Switch in DHW position
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Depress the ignition button on the boiler control panel whilst holding in the gas control knob on the gas valve and ignite the pilot.
Hold the gas control knob in for a further 20 seconds and then release. Does the pilot remain alight?