Set Appliance State:

WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Tap the      button, this will show current system pressure.
Is the pressure between 1.0 and 1.5 bar with the CH system cold?
Add a small amount of water to the system, does the pressure displayed increase?
Note:
If pressure on display does not increase take care not to overfill system.