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went 4a flush out of system this weekend - am now sitting in the cold!there was a lot of 's##t' in the tank and no doubt my system is full of it blocking all valves so that it wont even drian the system down!am awaiting a plumber to call to tell me possibly that i am going to need a new system! word of warning to all... look after your central heating systems, have lived in my house 4 over 5years and have never bothered with it and will now pay the price! further updates to follow! keep smiling!