Christian McArdle wrote in message
t...
1. Under what circumstances do you use a SINGLE non-return valve, and
when do you use a DOUBLE non-return valve ? What advantages/disadvantages
does one have over the other ?

Single valves are cheaper and drop less pressure. Double valves are more
reliable and required if water byelaws require a check valve, such as
before
a shower, or garden tap.

Thanks for the reply. I'd certainly agree with the comment about
reliability - I've had problems recently with my system's hot water loop not
maintaining temperature properly when drawing off eg for a bath, and this
was worse if the pump was switched off. When the pump was on and not drawing
water, I'd then also get a rattling noise. I finally traced the problem to
the single valve not closing properly.
So I'm changing it for a double !! (or was I just unlucky?)
Thanks again
Ron