"Jim K" wrote in message
...
On 11 Oct, 17:59, Terry Fields wrote:
Simon wrote:
http://picasaweb.google.co.uk/simon....terTankPhotos#

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

The photos strongly suggest you have the same sort of heating system
that we've just left behind.

This is a boiler that heats primary water (usually fed by a jockey
tank somewhere above the hot water tank) that circulates through a
heating coil in the HWT to provide domestic hot water, and via a gate
valve to the radiator system.

Helpfully, the photos show that this valve is marked 'heating system'
on the wall just above it. It's a racing cert that all your radiators
have thermostatic valves on them.

Normally, primary water from the boiler will circulate through the
heating coil in the HWT until the capillary valve (the one with the
thin pipe going to the sensor strapped to the tank) shuts down at the
temperature set by control knob.

Also, if the heating gate valve is opened, primary water will
circulate through the radiators until their TRVs shut.

With both the capillary valve and central heating shut off due to
reaching the set temperatures, the pump will still be running as it is
controlled by a timer. In this case the pump must not run in the
'stalled' condition, it needs to pump water continuously. This is
obtained through a bypass controlled by another gate valve, almost
certainly the one on the vertical pipe running towards the top of the
HWT.

As others have pointed out, if the bypass valve is too 'open' water
will preferentially pass through it rather than the heating coil in
the HWT, leading to a lack of domestic hot water.

Another problem is a fault with the capillary valve; either it is
stuck shut and not allowing primary to flow through the heating coil,
or the capillary or sensor is faulty leading to the valve not opening.

Try this sequence of fault-finding:

Unscrew the knurled ring holding the capillary valve head to the body,
and gently place to one side. If there is a plunger pin on the valve
body, gently try pulling it upwards with pair of pliers to see if it
is free. Use a folded rag to avoid marking the pin. Wick some WD40
down the shaft of the pin.

If there is no pin in sight, leave the valve head off.

Now shut the 'heating system' valve, ensure the boiler thermostat is
nat about two-thirds of maximum.

Turn on the system at the timer/control clock.

If the pipe both sides of the capillary valve gets hot, then water
will be flowing through it and the heating coil, and hopefully heating
the DHW. If there is no or little flow of hot water past the capillary
valve after say ten minutes (feel the pipes as far away from it as
possible), shut the gate valve on the vertical pipe, and then open
half-a turn. See if this makes any difference to the water hopefully
flowing past the capillary valve.

With the system running, the bypass valve almost shut, yet no hot
water flowing past the capillary valve, a fault in the body of the
latter is almost certain, suggesting replacement is necessary.

If hot water is passing the capillary valve, screw the valve head back
on and set it at maximum. Wait some minutes to see if hot water is
still passing through it; after ten or fifteen minutes the water in
the HWT should be heating up. If so, turn the setting to minimum. If
not, there may be a fault in the valve head, again suggesting
replacement is necessary.

Now. listening to the heating pump, shut the bypass gate valve. The
speed of the motor may increase as it is now doing nothing; crack open
the valve slowly until the speed of the motor drops to almost 'normal'
(when it is pumping hard). Although water will be bypassing the
heating coil, it should nevertheless be a limited amount. This water
is not 'lost', it is merely going back the boiler, but you only need
enough of it to keep the pump happy when it has noting else to do.

Hopefully this will have either shown up faults in the capillary
valve, and set the bypass valve to a reasonable setting.
Unfortunately, gate valves can get sludged up and although apparently
shut, may in reality still be partially open, confusing the picture.

Nevertheless, give this a try and see what happens - it might get the
system working properly, or at least give some pointers to where the
fault might lie.

If all is well, you can try fine-tuning the system by e.g. increasing
the boiler thermostat setting (quicker heating by the CH circuit) and
the setting on the capillary valve to give the temperature you want.

Good luck!

TF

good post!
Jim K



As I recall it was a cheap alternative to a motorised valve. The capillary
tube is strapped to the tank and this will close of the gravity feed to the
cylinder when it reaches the right temp - leaving the boiler output to be
solely for the central heating. I nearly fitted on about 35 years ago to my
back boiler system.