Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
CH Demand
Turn Hot Water Tap On
Isolate mains DHW at boiler isolation valve
Attach black lead to a suitable earth using a crocodile clip
Attach black lead to a suitable earth using a crocodile clip
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Allow the boiler to run in CH mode.
Place the red probe on pin 15 (green) on LV2
Monitor the voltage on the multimeter and open the DHW isolation valve - as the boiler recognises the DHW demand the multimeter display should be seen to fluctuate from 0 - 12 VDC a few times as the mode changes (some multimeters may show 0 - O.L or a negative voltage due to their response time - this is acceptable as are any voltage fluctuations on the multimeter display).
Does the voltage behave as expected?
Note:
The voltage will only be seen to flicker for a few seconds while the PCB switches between modes, repeat test from the start until you are confident of the result.
Place the red probe on pin 15 (green) on LV2
Monitor the voltage on the multimeter and open the DHW isolation valve - as the boiler recognises the DHW demand the multimeter display should be seen to fluctuate from 0 - 12 VDC a few times as the mode changes (some multimeters may show 0 - O.L or a negative voltage due to their response time - this is acceptable as are any voltage fluctuations on the multimeter display).
Does the voltage behave as expected?
Note:
The voltage will only be seen to flicker for a few seconds while the PCB switches between modes, repeat test from the start until you are confident of the result.
Isolate as per TOPs P4
and refit as necessary