"Tim Downie" wrote in message
...
snip

I wonder if you might have an old directional zone valve that has been
fittted the wrong way around? It may be that with a bit of slack
developing in the actuating mechanism, the ball in the valve is bouncing
on its seat?

Work out which way the water is flowing though your valves (feel for which
side heats up first when the system is turned on) and make sure that this
agrees with the direction indicated by the arrow (if present) on your
motorised valve.

Of course, if it was agreed that BG were supposed to replace the valves
anyway then get the idle buggers back to do the job they were paid for.

Tim

Tim, zone valve flow direction is correct. The system has been working
fine for many years. Thanks for the suggestion though.

p.s. I got a refund from BG for the zone valve installation that wasn't
carried out.

My worry is that BG is correct and my existing zone valves are just fine.

That leaves me wondering just what *has* happened with my system and
how to fix it.