On 17 Nov 2004 15:42:00 -0800, Peter Cherry wrote:

Hi, I've got a problem with a hot water expansion tank overflowing
at a property I let out. Its a 5 yr old GCH gravity system i.e. the
type that must heat the hot water when the CH is on. The tank that
is overflowing is the large hot water expansion tank in the loft not
the small C/H tank.

snip rest of excellent posting describing tests and results already
done

You've already gone through the common causes:

Hole in cylinder coil (though that normally causes the CH header tank
to overflow as it normally has the lower water level being a smaller
tank).

Expansion would only happen as the system heated up from cold, how far
below the overflow is the water when the ball valve shuts off? If it's
more than a couple of inches on a 50 gallon tank thats a heck of a lot
of expansion.

Does the overflow happen in the middle of the night a few hours after
the last ho****er is drawn or when the boiler fires up in the morning.

Is the flow constant? Expansion would stop once everything is hot.

I think the mixer points are worth a very close look, probably not the
kitchen one as that should keep the hot and cold seperate right to the
nozzle and any leakage past the valves would come out the spout and
not up the HW pipework... A worn out O ring or housing in the shower
seems favourite at the moment. As another poster has suggested does
flow of water into the tank stop if you turn off the rising main?

--
Cheers
Dave. pam is missing e-mail