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.
--
Cheers,
Roger
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