Boiler doesn't relight?

europa boiler 24/28.
Over time the water pressure would drop - when below the minimum bar pressure the green (led) would change to red and then, when running the hot tap, the boiler didn't fire anymore. Bringing the water pressure up again changed the red light to green and the boiler would fire again, until this week - even pressing the reset button won't bring the green light on anymore !
What's gone wrong and what needs to be done now ?