In message , Roger Mills
writes
On 08/10/2010 10:55, Simon wrote:
http://picasaweb.google.co.uk/simon....terTankPhotos#

this is the third time i've tried to post this link. third time
lucky!!!!!!!!!!!


OK, that tells us a bit more.

One thing which may be significant is the gate valve which can be seen
in photos 23 and 29 (among others). The pipe in which that valve is
fitted appears to be some sort of by-pass across the cylinder's heating
coil - maybe so as to provide a flow path when the TRV-like valve
closes. How open or closed is that gate valve? (Count the number of
turns required to close it from the current position, and then the
turns required to open it fully from closed, to give a measure of its
current state). If fully open, it provides a dead short for the coil -
with the result that nearly all the primary water will go down the
by-pass and very little through the coil - which could well explain
your problem.


I'm not sure if we ever heard if the tank was actually getting hot or
not (or was there some other problem after the tank with the HW) - a
quick hand test on the metal of the tank will confirm. (near the top of
the HW tank obviously)

If it isn't then the capillary valve would seem like a prime candidate
for failure of some sort (either valve or capillary tube/sensor).
Presumably they are like a TRV inside. If you remove the top (ours has a
knurled ring at the base of the body you unscrew) then presumably it
just leaves the valve open. That would be my first try.

I'm not sure about how they actually work, but assuming they have a pin
operated by the capillary senor, this could be stuck like the ones in
TRV's do.
--
Chris French