Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Ensure system pressure is set between 0.6 and 1.5bar
Remove control box cover if necessary
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the red wire from the low pressure switch on X22 and the neutral at the incoming mains terminal strip, with the connector X22 attached to the PCB.
Expect approximately:
1.3vdc at 0.6 bar and 2.5vdc at 1.5bar.