Baxi Solo 3 heats water but not CH?

My 5 year-old Baxi Solo 3 CH circuit has just packed up, although the water heating is fine. The CH is controlled by a wireless Drayton Digistat from the lounge. I replaced the batteries a few months ago. The Siebe Lifestyle mid-position valve is positioned too close to wall to manually select both ports. Could this be a valve actuator fuse blown in the junction box, or has the thermostat packed up ( the actual temp is shown as 10C less that set temp, and a green light is continually showing on the receiver though the boiler does not start). Would be very grateful for some advice before I call in an "expert".