Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
CH Demand
Boiler ON/OFF Switch OFF
CH Temperature Selector to Max
DHW Temperature Selector OFF
CH Temperature Selector to Max
DHW Temperature Selector OFF
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Boiler ON/OFF Switch ON.
Measure Voltage across the connections of the Modulating Solenoid (blue wires).
Measure Voltage across the connections of the Modulating Solenoid (blue wires).
Isolate as per TOPs P4
and refit as necessary