Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
Gain access to PCB (use Insulation Mat as required)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage at pin 6 of X7 on the PCB to a suitable earth point.
Voltage depends on system pressure.
Pressure on DisplayVoltage
0.0 bar0.5V DC
0.5 bar0.9V DC
1.0 bar1.2V DC
1.5 bar1.5V DC

Does the voltage measured approximately match the pressure on the display?