Combination of Sod's law, clustering of random events, problems of combis
once they get past five years IMHO.

In the past month mine has:

blocked a DHW HX (fixed)
failed the ignition circuit on the main board (fixed)
split a DHW flow sensor diaphragm (fixed)

and in the course of all that, the auto air vent decided not to seat, so it
was dribbling water. Took out the valve and cleaned off the scale
mechanically; now it doesn't leak, or vent either. Waiting for a new
one.....

Oh, it's a Wickes / Halstead. But the preceeding Vaillant behaved much the
same after eight years.

Makes you think about signing up for BG service.....