On 16/10/2010 15:17, Simon wrote:

Hi,

I did the test with the settings as suggested by Terry: ie, bypass
valve a quarter-turn open, heating valve completely closed, gas boiler
thermostat set on 4 (max is 5), TRV-like capillary valve fully open).
After half an hour the tank was slightly warmer (you could feel it was
a bit warmer but not much and certainly not near "hot"). The pipe
going from the tank to the TRV capillary valve was somewhere between
"no difference" to maybe "slightly warm"), but the pipe going from the
TRV capillary valve off to the top tank and the rest of the system was
very hot (too hot to touch). Is this the way it should be?


After how long? The return from the coil won't be very hot until the
water in the cylinder has heated up quite a lot - whereas the by-pass
*will* be hot if there's water flowing through it.

After 30 mins I ran the bathwater and the water was warm but not
enough for a bath. After 90 mins I ran the bath and it was running too
hot to touch and there was enough for a bath.


It shouldn't take 90 minutes to heat a tankful of water. It may take
more than 30, but even then, the water at the top should be hot.

So... yippee!!! Many many thanks Terry! This is the first time we have
ever been able to have a hot bath without having the electric heater
on for more than an hour (usually 90mins min). Just this on its own
will save me a fortune and make life so much easier. All i need to do
now is try the gas boiler thermostat on diff settings for diff lengths
of time to find the optimum setting for water temperature, time to
heat, and units used etc.

But... from the above, is this HW system now working well or should it
be better?


It should be better!

btw - When I say "gas boiler thermostat" set on 4" I presumed you
meant the actual dial-setting on the boiler itself, and not something
on the water tank or associated pipework. Is this right? I couldn't
see anything else on the tank that could be adjusted and so I presumed
that the dial setting on the boiler was what you meant.


Yes, I'm sure he meant the boiler stat.


Because of the success of the above test I didn't remove the top of
the TRV-like capillary valve and see if the pin was stuck in a
partially closed position, from the above do you think this is
necessary or a still a good idea?


Yes. I suspect that water still isn't flowing through the coil as fast
as it should. Try running with the thermostatic head removed, having
made sure that the pin is fully up.

Because the water can reach boiling in the tank I guess it means there
is a failed thermostat that needs replacing as you say, and this is
something I should look at (even though i presume limiting the heat is
purely a safety measure, and is not something that is done for the
efficiency or otherwise of the system).

It is an extremely important safety measure - particularly when you have
a plastic header tank in the attic (which you don't appear to have).


When we move into winter and we want to have the radiators on for at
least part of the day, will it be okay to switch between having the
heating valve fully open to take the heat of the gas boiler to the
radiators, and then close it fully to heat the water for a bath, and
then after the bath to open the heating valve again to heat the
radiators, or could this cause problems? Is it okay to simply switch
between fully open and fully closed in this fashion?


I think you should seriously consider upgrading the controls of your
system by replacing the manual heating valve with a motorised zone
valve, and replacing the TRV-like cylinder valve with a zone valve plus
cylinder stat, with independent timers for each circuit - in other
words, convert it to a proper S-Plan system.
--
Cheers,
Roger
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