CH/HW splitter T-piece with motorised component

[judder]

Sorry for the topic title, but I don't know the proper name for the part. In my airing cupboard, I have a pipe going to the HW tank and another heading off to the radiators (I assume), both being fed by a pipe coming from the pump, making a T-junction. On top of this T is an electrically operated device which (I think) is supposed to turn a valve to open the CH pipe, the HW pipe or both.

1) The motorised unit is always hot (and I mean always, regardless of how hot the water is, or how long the boiler has or hasn't been running). It's as if there is a continuous electric current running through it. Is this normal?

2) I have no independence between CH and HW, i.e. if one is on, so is the other. I'm guessing that the valve in the T-junction must be stuck, open to both CH and HW. Is this likely to be something to do with problem (1)?

Thanks in advance.

 

[shambolic]

If it is a silver box on top its a honeywell Mid position valve The motor inside will be seized.
Need more info such as make and model or post a photo of it!

 

[judder]

Thanks. I'm at work just now, but will look for the model number and try to get a picture up later.