Went and had another look earlier, removed diverter motor and yes pin was moving in and out with HW/CH demand. Checked pin in diverter body wasn't jammed aswell. Noticed that CH seems to work ok, then turn a hot tap on and switches over to HW ok but when it has to switch back to CH boiler...
HW working ok. CH not working! Last week CH started to be temperamental. Heating switched on and rads hot then all of a sudden heating still on on integral clock but rads would go cold. Then would switch heating off on clock but pump would keep running for hours. Now heating will only fire up...