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I've just found an entry on AGA Central Forum about someone using this company to repair the control board on a 30 Amp AGA.
As I want to make sure I remember it if I have the same problem on my 30 Amp AGA here are the details:
30 Amp AGA Control Board Repair Company RadTronix offer a 3 day turn around of repair of control board for 30 amp AGA. www.radtronix.co.uk with 12 month warranty on repair.Google+