"Toby" wrote in message
...
A valve that will only open to either one port or the other is known
as
a
"diverter" valve. Those that can divert and allow flow to both ports
are
called mid-position. Diverter valves are simpler and the best choice
if
only diversion is required.

See for a Myson diverter valve.
http://tinyurl.com/g5xz

Or the Drayton ZA5, includes a limit switch. At rest Common to port A,
energised Common to port B.

The limit switch is very handy, as many diverters do not have them.

The mid postion seems to be given precedence to the diverter in the
merchants, my local CIty Plumbing only do the diverters 'to order'.

Unfortunately that is the case. It is best to use a diverter and a quick
recovery cylinder that takes all of the boilers heat, rather than a
mid-position valve. The cylinder will re-heat in quick time and make no
effect on the house heating for the short time it is re-heating the
cylinder. Quick recovery cylinders use less gas overall, and can be
downsized as they re-heat so fast.


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