is it a combi? have another look for another name as im not familiar/dont think there is a model called 500, usually have a brand (vaillant) model name and a number to represent the size. Is there a plastic/rubber or silver flexible hose joint between 2 of the pipes connected to boiler? if so, its prob just a case of turning taps off. do a google image search of boiler filling loop and you'll see what i mean. if a combi, theres a chance its more serious and expensive. unsure without more details of boiler im afraid
mr gas, December 2010
