CH comes on when only Hot Water selected

I think this my problem may be related to a motorised valve which sits at the junction of the HW and CH circuits which is either stuck or needs replacing. Any suggestions as to how this can be fixed? Can I do this myself - I am not a plumber or CH engineer!!

Yes you're probably right. Have a search & read, & tell us what make it is and what details you can.

Thanks for the reply. I have got a bit more info from the valve itself. I believe I have a Sundial Y PLan central heating system (it says this on the valve). The valve is described as a 3 position diverter and was made in Canada. The valve is wired into a junction box on the floor of the airing cupboard - so I suppose these could be a problem there. Is it worth diconnecting this and attaching a plug to the wires and plugging into the mains to see if the pump does anything on a different electricity supply? If the pump is completely dead, is this something I can swap out myself easily or does it need a lot of other work as well (e.g. drain down CH system etc)? Many thanks

But you said your CH was working...??
Yes you can connect a 3A fused mains supply to the pump. If not sure if it's running, change the speed and you should hear it.

Sorry if I am confusing things. Yes CH and HW both work fine but when I select HW only at the control switch I get both HW and CH!

Thinking about it, could the diverter valve be stuck in the HW and CH position? Would tapping it gently with a hammer possibly free it up? I could try this first and if that fails I could try wiring it to a different 3A circuit?

Just got home and checked valve - it's quite hot even though the DH and HW have been off all day!! Tried tapping the valve to release but nothing. Reckon the motor is burning out so will look on ebay for a new one and swap it over.