i am not telling you off at all. Actually i don't understand now - i thought you didnt have a tank with a combi - we certainly don't. As far as i know (of course i could be wrong) my boiler runs of the cold mains supply, and when i turn the hot tap on, cold water comes out of the mains and gets heated by my boiler immediately. this means if i had unlimited fuel i could have as much hot water as i needed/wanted, whereas with a tank i am limited to how much the tank holds