Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Boiler On
SUMMER/WINTER switch set to the WINTER position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the DC voltage between F11 (+ve) and F15 (common) on Full Sequence board.