"Christian McArdle" wrote in message
. net...
...You put a check valve on each CH zone to prevent back circulation.

Please explain what a check valve does - any weblinks with nice
pictures?

It's a one way valve. A standard check valve needs too high a pressure and
can be very noisy in this application. Instead, you need a much harder to
locate flap type valve, preferably unsprung.

Christian.

Running two CH circuits from the store of water, there is no need for check
valves. Not all check valves buzz.


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