Set Appliance State:

Mains Power Off
Set Multimeter to AC Volts Set meter to measure AC Volts
Turn Hot Water Tap On
DHW temperature control to maximum
CH temperature control to minimum
WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Boiler ON/OFF switch ON.
Measure on connector M1 the voltage across the brown lead (Live) and blue (Neutral) on the PCB.