"Julian" wrote:

Hello Julian

J| When you say hosepipe on the drain I suppose you mean run
J| the system with the drain open and somebody in the attic
J| making sure that the header level doesn't get too low?

Nono, the other way around. The method is the same as backflushing a
hot water tap.

You connect a hosepipe to the drain connector of the CH, open the
drain and turn on the hosepipe's tap. Forces water back through the
system (although by the shortest route, so won't get an airlock in a
badly designed system).

The reason I say to have someone watching the header tank is indeed to
stop it overflowing. It should have an overflow pipe, but quite often
these are undersized and/or blocked. Don't trust just this alone!

--
Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk/