Glow-worm 30ci problems?

my 30ci keeps losing pressure which i think is the pipe going to the exp vessle but it also does not give me hot water just warm enough for a shower, while producing hot water it makes a noise like it is seperating the water flow and the pipe to the rads gets hotter than the water for the shower the diverter valve was taken out and some silicon grease used because it was a bit stiff which did work for a while.
i did buy a new valve but the one in my 30ci screws in and the one supplyied used a clip is there two different types? and more ideas? all help welcome