Set Appliance State:

Boiler in standby ('0' on display)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Apply CH demand.
Does appliance respond to demand?
(i.e. does status code on display change or pump/fan begin to run)
Note:
If display has turned off (just showing one or two dots) tap   to display status.
(Click here for the list of boiler status codes)