"David W.E. Roberts" wrote in message ...

Combi boiler (no header tank)?
Traditional (hot water cylinder, header tank)?
What kind of system is it?

Sorry, was in a hurry to post !

Yes, it is a traditional gravity pump system.
Installed 2001 by the wonderful BG.
Boiler is BG-branded F2 (Potterton?).

In answer to the other post, the gas supply definitely wasn't switched
off.

Update:
-------

Gets more bizarre. I thought it would be unlikely to be the boiler,
but when I eventually went to take a look, the boiler had switched off
(boiler is in garage).
The boiler has an Overheat Limit Thermostat, which appeared to have
tripped. I had to reset it by pressing a recessed button on the
underside of the boiler casing.
By resetting this thermostat, and powering the boiler off and on
again, I managed to get it to light. This worked fine for the rest of
the day, and we had heating and HW throughout.
Overnight, however, the system wouldn't switch on at the programmed
time. Had a look at the boiler again this morning, same story - it had
switched itself off.
Same procedure sa yesterday lit the boiler temporarily, but the CH+HW
wouldn't get going. The boiler also cuts out after a few minutes, with
quite loud spluttering and banging.
The pump+valve are in the airing cupboard above thestairwell, along
with the HW cylinder. When I switch either function on, there is a low
grinding noise for about 45 secs, then a constant very low rumble for
the next few minutes, then silence. Looks like the pump is trying to
turn itself over, but can't.

Any help please, or is it best to have someone in to look at it ?
Can't really do w/o CH with the kids at home.