Arriston combi boiler hot water scalding temp light comes on?

high temp light comes on, boiler cuts out, click reset button works fine.. then cuts out few mins later. bar pressure is correct.
we have noticed that hot water flow from tap higher pressure than it used to be. never had water this hot which is great but boiler cuts out. used to have to turn tap to reduce flow for hot water. even with hot water heat control on lowest setting still scalding hot.. is it just a question of replacing temperature switch, had so many things replaced over last few years should be like a new one. in the past have had a switch replaced, think diaphragm in a valve, gas valve, circuit board. similar problems. surely its a switch not cutting temp off at given point. ideas please. very capable of replacing any part, except i wont touch gas side of it...