"Phil Addison" wrote in message
...
On Tue, 11 May 2004 09:30:16 +0100, "Bob Mannix"
wrote:
"Chris Hodges" wrote in message
...

I've got a cold cistern (in the loft) which just feeds the bath cold
tap and the inlet into the hot cylinder. After going up to put some
fernox
in the F+E tank I noticed that the expansion pipes for both the loop
(i.e. boiler, rads + heat exchanger in cylinder) and hot water (taps)
discharge into the cistern.
...
How much of a big deal is this? There's no easy way to tell which pipe
is which to divert one into the F+E (which doesn't have much value in
terms of expansion).

"Phil Addison" wrote in message
...

An easier way is the reverse! Bung up the pipes and see which one
STOPS
the water flow out of the hot tap. Get a pair of Drayton bungs - they
are conical and will fit into 15 and 22mm tube (but not 28mm). Put one
in the exit pipe of the domestic hot water header tank - that will be
under water at the bottom - and the other in one of the vent pipes.
Then
turn on a hot tap in the bathroom. If you have the correct one no
virtually water will flow. If you have the 'wrong' one, the contents
of
the pipework from the tap up to the open vent will flow out, just a
few
pints.

If the bathroom is downstairs, leaving the hot tap on with the pipes
blocked
will result in the collapse of the domestic hot water tank - a frequent
occurrence in winter where the two pipes are frozen. Depending on the
height
of the tank you may have a problem with an upstairs bathroom. You may be
OK
if the tank is very old (they were a lot thicker then). A rather risky
technique! If you must use it, as soon as the water slows (ie you notice
an
effect) shut of the tap and remove the bungs (or one at least).

Good point! I sort of had that in mind when I said bathroom, and meant
an upstairs one. But yes, do be careful as Bob says. It would be a good
idea to have someone watch the tank, ready to yell if it shows any signs
of inward bucking.

Revising the idea, how about blocking just the header outlet with a bung
and then have someone turn on the bathroom tap. Then test which vent is
drawing in air. This could be by putting a piece of cloth over it to
test if it tends to be sucked in, or maybe by just listening. Don't use
the palm of your hand to test for a vacuum as it could be quite a strong
one, and the cylinder might buckle with you stuck to the vent. Probably
not though.

Or better: Block off the header outlet as above (don't block the vent),
then run the hot tap till the flow stops. Any tap will do, there is no
risk this way even from a downstairs one. Then turn off the tap. The
vent pipe will now be drained down to the level where it joins the top
of the hot water cylinder. Now head back to the loft.

With the header bung still in place, put the other bung in one of the
vents. Now remove the bung from the header. This will cause the emptied
vent pipe to refill with cold water and if you picked the right one it
will compress the air in the vent above it. You then pull the bung out
and you should hear a decent pop of air rushing out if it is the right
one. You could probably detect which one has the air issuing without
bothering with the bung.

snip

what about taping a balloon (or balloon equivalent) onto the end of the vent
pipes and see which one reacts?

Probably safer with revised method 2 - you wouldn't really want it being
accidentally sucked into the DHW tank!



--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk