On Tue, 09 Jan 2007 00:57:07 -0800, russ.elliott wrote:

Thanks chaps, John can you elaborate on your last paragraph? I don't
quite understand as CH is a new area for me....Cheers

Systems are often set up so that when water is going round the cylinder
the rads don't necessarily heat up very well since the cylinder is taing
most of the flow, but it doesn't matter since by the time you notice it
the cylinder has heated up and the flow to the cylinder has cut
off again. If the cylinder stat is stuck on then water will always
be going round the cylinder so circulation to the rads continues to suffer
and you do notice it. That's why I asked if it's a new problem.

If you turn the cylinder stat control down does the pipe taking water into
the cylinder coil from the CH system (via 2- or 3-port valve) cool down
after a while (maybe 1/2 hour)?