On Mon, 07 Jan 2008 16:52:22 GMT someone who may be
wrote this:-

Not true, there should be a double check valve at the boiiler inlet to
prevent the system contents from backflowing into the mains.

The double check valve is slightly better placed on the mains side,
to prevent the rather remote possibility of back siphonage via the
filling loop. It also allows draining/relieving pressure via the
filling loop. The disadvantage is that it allows those with
inquisitive fingers to turn an easy to turn valve and allow hot
water out under pressure.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54