Set Appliance State:
Set Multimeter to DC Volts 
Turn Hot Water Tap On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Reset boiler if required.
Measure for DC voltage across pin 3 (pwm) of connector X16 and a suitable earth connection.
Voltage measured should be approximately 4.0 Vdc or greater & increasing as time elapses (see note).
Note.
Connector & pin numbers are printed on the PCB.
Measure for DC voltage across pin 3 (pwm) of connector X16 and a suitable earth connection.
Voltage measured should be approximately 4.0 Vdc or greater & increasing as time elapses (see note).
Note.
Connector & pin numbers are printed on the PCB.
Isolate as per TOPs P4
and refit as necessary