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
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the red wire (7th up from the bottom at connector X22) from the low pressure switch and the neutral at the incoming mains terminal strip.
The Voltages should conform to the table below:
Pressure (Bar)DC Volts
0.51.1
1.0 1.6
1.52.5
2.03.1
2.54.1