DHW too hot? Help please.

Hi all,

I have a open vented central heating system with an indirect cyclinder and a concord wrs 255A boiler. Currently the DHW is boiling hot. I recently replaced the thermostat on the cyclinder as the temperature dial on the old one broke off. It appears to have made no difference. I have on a pipe coming out of the cylinder what looks like a motorised valve (no markings on it unfortunately). There is also a zone control valve (2-way I believe) next to the boiler downstairs. The thermostat on the boiler is set to 2. My boiler keeps firing up every 30mins or so (central heating turned off). Can anyone explain what could be the cause of the too hot water? I don't quite understand what should control what. What exactly would the thermostat on the boiler control?

Thanks for your help[/img]

One of the motorised valves is stuck. Post a picture for more help.

Ok, pictures of the system can be viewed here: http://dnunez.bulldoghome.com/photos/BDRES/dnunez_bulldoghome_com/

The 1st & 2nd pic is of the boiler and boiler control. The 3rd is of the motorised valve next to boiler, the 4th is of what I believe to be a motorised valve attached to a pipe coming from the hot water cylinder and the last picture is of the same, but with the cover taken off.

Hope some one can help.