On 2020-10-08 10:24:50 +0000, John Rumm said:

Quite possibly - but it also explains why a number of installations
seem to work in practice, even when they their supply pipework is well
out of spec.

So our new Vaillant has conked out tonight after working perfectly for
a week. Won't fire up, just like the old Vaillant now scrapped, which
also failed on a Friday evening.

It seems to be a gas valve issue and I hope it is and not intolerance
with the supply. The only other gas appliance we have - a 5 ring gas
hob - is working OK.

So all I can do is call out Vaillant under their warranty as the
installer can't touch it without voiding the warranty.

This is distressing for the family...