Good point, David.
Boiler was installed in c.2000 and has always been fine, with the exception
of the stated replacement of the pcb which would have been probably 4 years
ago. No plumbing circuit changes, nothing different at all. The boiler is
the only gas appliance.
It's not until very recently that we've turned the CH on; it's possible that
the DHW problems described started around that time. Since we noticed a
problem c. two weeks ago it's got more pronounced.
Cold mains pressure is very good.
Thanks