Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Purge Switch in NORMAL position
HW Switch in ON position
CH Switch in OFF position
HW Potentiometer set to mid range
HW Switch in ON position
CH Switch in OFF position
HW Potentiometer set to mid range
Gas On
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow the Burner to operate at Full Rate approximately 16 mb and heat the Domestic Hot Water.
Measure the Voltage across the two Violet wires on the Gas Valve Modureg Solenoid.
When the Domestic hot water has been heated sufficiently the Modureg Solenoid Voltage should vary according to the HW potentiometer setting.
i.e.. When the HW Potentiometer is turned up the voltage should increase when it is turned down voltage should decrease.
Note:
The DHW flow may need to be reduced at the tap to assist temperature rise.
Measure the Voltage across the two Violet wires on the Gas Valve Modureg Solenoid.
When the Domestic hot water has been heated sufficiently the Modureg Solenoid Voltage should vary according to the HW potentiometer setting.
i.e.. When the HW Potentiometer is turned up the voltage should increase when it is turned down voltage should decrease.
Note:
The DHW flow may need to be reduced at the tap to assist temperature rise.
Isolate as per TOPs P4
and refit as necessary