In message
,
Simon writes
On 8 Oct, 22:05, Roger Mills wrote:
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.

If it's open a long way (or fully open even) try running with it only
open a little - maybe half a turn from closed) and see what happens.
If you *need* a by-pass at all - and you may or may not depending on the
requirements of the boiler and on how the system 'controls' are
configured - you'd be far better off with a spring-loaded auto by-pass
valve which only opens when it needs to, rather than a manual gate valve.
--


many thanks for your reply. the gate valve directly above the TRV-like
valve in photo 23 was fully open. It took seven full turns to make it
fully closed so I have turned it six turns and put on the gas boiler
to see what happens. I will post and let you know.

btw - to clarify: the gas boiler has not been heating the water above
tepid. I had the gas boiler on max for one hour and the hot water was
barely warmed at all. Because of this I have been using the electric
heater to heat the water, which it does but it takes about 90 mins to
make a hot bath, which costs a fortune. When the electric heater has
been left on accidentally, the water boils merrily, filling the attic
room with condensation. For this reason, I am fairly sure that there
is no temperature sensor cut-off system in place for hot water tank.


The latter issue of the water in the tank boiling when using the
immersion heater is almost certainly due to a failed thermostat
controlling the immersion heater (this is all separate from the temp
control relating to heating it via the boiler). The thermostat is cheap
(about a tenner) and easily replaced.

This page show what is involved:

http://www.diydata.com/problem/immersion/immersion_heaters.php

Re the problem of heating via the boiler, I suspect the culprit might
be the TRV-a-lke/Tapstat . It sounds to me as if it either has got stuck
in a mostly closed position. Radiator TRV's do this qiute often.

I guess they are basically the same inside. If you remove the head of
the valve - at the base of the white body of the top of the valve should
be a metal ring. This can be unscrewed (might be tight and need
pliers/wrench to start) and then the body removed. Inside you should see
a pin sticking up. This pin can stick - typically with the valve closed
so stopping it operating. You should be able to push it up and down. f
you can't you can use pliers to wiggle it or gently tap it to free it
up. If it will move freely than leave the top off this should leave it
open, and then hopefully then water in the tank will heat up
--
Chris French