Set Appliance State:

Mains Power Off
Gas On; Pilot On
Turn Hot Water Tap On
Rotary Switch to DHW position
DHW Temperature Control To Maximum
Hold in Boiler Case Switch
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

After a suitable period with the burner at high flame, slowly reduce the DHW Temperature Control setting to a minimum. Does the burner flame reduce in size?