Set Appliance State:

Mains Power Off
DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
Loosen the outlet test point screw (P2) and attach U-gauge to the test point.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With the hot water tap running.
Does the burner light and go to maximum burner pressure
(approximately 8mb) after a few seconds?
Note: When the U-gauge is removed, ensure the pressure test
point is checked for soundness.