Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
Locate primary system filling loop
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
1. Measure for DC voltage across pin14 (red lead) of connector X2 and a suitable earth connection, make a note of the voltage measured.
2. Increase the primary system pressure slightly, measure the DC voltage as above, has the voltage increased after an increase in system pressure?
2. Increase the primary system pressure slightly, measure the DC voltage as above, has the voltage increased after an increase in system pressure?
Isolate as per TOPs P4
and refit as necessary