I have a potterton 80 which has been playing up. Water has been coming out of the discharge pipe into the garden. I have been told there is a possible faulty with the expansion vessel. It have also been suggested to fit X200 which I bought from ScrewFix which I have done, now making me have to reduce the bar pressure of 3 down to 1 by removing three cups of water from the radiator system three times in seven days. Am I correct in doing this and approximately how long will I have to countinue reducing the 3 bar pressure? If this doesn't work, how difficult is it to fit a expansion unit to the potterton 80 as looks like the expansion unit is located behind the heat exchanger etc? or is a external one easier to fit and how?