Set Appliance State:

Mains Power Off
Set Multimeter to DC Volts Set meter to measure DC Volts
DHW Demand
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure for DC voltage across the red lead (DHW turbine connector) and terminal 2 (blue) main terminal block.
Expected voltage approximately 1.8 - 2.5 Vdc.
Note:
Due to the positioning of the DHW turbine it can be difficult to
obtain a reading. Ensure a good connection is made.