On Mon, 08 Jan 2007 09:03:48 -0800, russ.elliott wrote:

Strange CH issue, when the hot water is off at the control panel, the
rads are all working fine and are hot, if the hot water also comes on
at the control panel the downstairs rads become cold. I have bled all
rads flushed the system, balanced the system and turned up the pump to
setting 3....any ideas much appreciated

Is it a new problem or has it always been like this? If the latter I'd
suspect balancing, and that the hot water is taking flow from the system
enough to starve the upstairs rads but not the downstairs ones. There may
be a balancing valve - probably a wheel-head gate valve with - in line
with the HW cylinder which you can adjust to balance.

If it's a new problem I'd check the cylinder thermostat which may
be failing to switch off and stop water going round the HW circuit when
the programmer is calling for HW.