Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Selector Switch Winter position
Gas Control Knob in Main Burner position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the Water Pump voltage across connections Pump L (Brown) and Pump N (Blue) on connector CN2.
This should be approximately 240 Volts AC.