No heating unless water is heating

[unwaith]

Hi there,
My central heating will not work independently of the hot water. In order for my radiators to heat up I have to set my controler to heating & hot water, and turn the hot water cylinder thermostat to its maximum setting to get heat from my radiators. I'm thinking the problem lies either with the 3 port valve or the central heating control box? Can anyone tell me if I am thinking along the right lines, or am I completely wrong? If it is either the valve or the controler, is it easy to identify which needs replacement?
Hope somebody can help, and thanks in advance for any assistance.
Paul.

 

[dontknowitall]

Try fiddling with the zone valve. If you can move the lever manually and it behaves as it should (hot water alone/heating alone/both together) then it'll be the motor inside (about 90% of the time).