I recently bought a house with a eurocal Combi boiler installed. The expansion vessel (orange pancake model) was faulty so ordered a new one an engineer fitted it. After 1 week it failed with water entering the gas filled side of the vessel, this was replaced again at no charge under guarantee. Now pressure dropped on system and engineer told me how to refill, however water does not fill system just goes straight out through pressure release hose. Any ideas why expansion vessel keeps failing, as I cannot afford a new one every 2 weeks.