Set Appliance State:

Use Insulation Mat as required
Set Multimeter to DC Volts Set meter to measure DC Volts
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch to Water
Adjust flow rate at tap to approximately 7 l/min
Gain Access to PCB
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to ignite and heat DHW to approximately 55 degrees C.
Measure the voltage between connections 1 and 3
(two yellow wires) on connector X16 on sequence PCB.
Does the voltage reduce as the DHW is met?