Observation:

The code numbers reveal what the appliance is doing during different stages of an operating cycle.
The following are the stages for heating operation:-
S.1 - Fan running and proving
S.3 - Ignition
S.4 - Burner operation heating
When external heating controls are satisfied the following sequence appears:-
S.5 - Pump and fan overrun
S.7 - Pump overrun
S.8 - Anti Cycling Control
S30 - External controls satisfied
When a hot water tap is opened, the boiler display will go through the following stages:-
S.10 - Calling for operation: d.h.w.
S.11 - Fan running and proving
S.13 - Ignition
S.14 - Burner operation: d.h.w.
When all hot water taps are closed, the boiler switches to heating mode if there is a demand.
If there is no heating demand, the following sequence appears:-
S.15 - Pump and fan overrun
S.17 - Pump overrun
S. 0 - No demand: d.h.w.