I have a Chausson which has a shower with a mixer tap on it, I am a bit scared of this because it is plainly dodgy . The valve is very difficult to set as the temperature varies from warm to bloody hot without touching it. Not the best thing to happen . What I need to know is there a proper thermostatically stable valve that I can fit, and where actually is the valve? I think it must be behind the plastic wall and would be major rip downs to get to unless there is another way or place to put it. Any ideas????