John wrote:
"Andy Burns" wrote in message
...
On 18/11/2007 15:47, John wrote:

Have you actually done this, i.e. EMPTIED the hot water cylinder via a
cold tap?
You shouldn't be able to /empty/ your hot water cylinder through a hot
tap, let a lone a cold tap.

I must ask why you think this, If the main stoptap into the house is turned
off as the OP stated and a hot tap is opened then the cylinder would
eventually empty (apart from the dregs in the bottom), unless my
understanding of gravity is wrong!

I think your understanding of gravity may actually be wrong! ;-)

Conventional HW cylinders draw off hot water from the top. The only way
to get it out of the top is to feed more (cold) water in at the bottom.
Hence it is never possible to empty it from the top connection - it
remains full no matter how much water you draw.

Usually the connection to the bottom of the cylinder from the cold
cistern is a dedicated one. I can just about visualise a plumbing error
that instead uses one feed to provide this and then continues to supply
other cold outlets in the house. In this case it might be possible to
drain a hot cylinder if you tied up the ballcock on the main cistern,
opened a hot tap to allow air in, and then opened a cold tap well below
the height of the hot cylinder.


--
Cheers,

John.

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