Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to DC Volts Set meter to measure DC Volts
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

Measurement:

Measure approximately 25V DC between L/H connector on Gas Solenoid Valve and Green wire of Flow Valve microswitch.