Set Appliance State:

Mains Power Off
Selector switch in heating & hot water position
Ensure there is no demand for either CH or DHW
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

When power is switched on the display should operate and follow the sequence below:
The blue light will illuminate and the display will show 8, the display will then show a rotating dash followed by the model of boiler displayed one digit at a time, either 24c, 30c or 35c (if the display does not progress from the figure 8 CLICK HERE).