Dear all,

I need some help diagnosing a problem I have with my hot water system.

I've got a cylinder tank in the airing cupboard which has above it two
square tanks, one large one small. I believe the larger is called the
feeder tank. As hot water is drained from the cylinder tank water is
drained from the feeder tank into they cylinder, which in turn is filled
up from the cold water mains supply up until a certain level (about a
1.5 inches below the overflow) at which point the float valve closes.

This all seems to work as described. If I don't use any hot water for
about 4 hours though the water level in the feeder tank has reached the
overflow and starts trickling out. It's a tiny, tiny trickle, so much so
that the water doesn't pour out of the end of overflow pipe but trickles
out the end, back along the bottom and is absorbed by the wall. The
plaster on that wall is blown. :-(

At first I thought that the float valve was shot, so I put in a
replacement, but that hasn't changed anything.

Any ideas as to what the problem might be, or what I should try next?

Many thanks

Andrew