Set Appliance State:
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector Switch in DHW position
Selector Switch in DHW position
Gas On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
With the DHW tap fully open measure the DC voltage on the black 2/3 solenoid.
The voltage obtained should be approximately 24V DC.
Decrease the flow at the DHW tap to assist temperature rise, does the DC voltage measured drop to zero as the DHW demands a reduction in burner output?
The voltage obtained should be approximately 24V DC.
Decrease the flow at the DHW tap to assist temperature rise, does the DC voltage measured drop to zero as the DHW demands a reduction in burner output?
Isolate as per TOPs P4
and refit as necessary