Release the pressure Via the PRV first otherwise you could get burnt by scalding hot water., you have the old style switch fitted , pull out the metal pin and then pull out the old switch, the new switch will be diffrent, you will have to remove the brass fitting (that he pin fits into) from the manifold, make sure you use TWO spaneers to do this (one as a hold against). the new switch screws directly into the manifold (use PTFE tape on thread) wiring is straight forward.
www elanar.co.uk (Grant Service Agent South East), October 2009