Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Voltage Set meter to measure AC Volts
Turn Hot Water Tap On
Summer/Winter Switch set to Summer.
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure voltage across pins 14 (+ve) and 13 (neutral), middle right on PCB.