Hi Martin, just had the same problem with mine because I spilt some gravey on to the burner!!, whilst cleaning it I must of move a small probe that needs to sit just above the flame, you can find it on the right hand side of the burner. I have had a man out today who put it back in place, he also turned up the valve at the back, since he did that I have noticed that the flame won't turn down now LOL! so it is all or nothing, I have just rang the man and told him and he has told me that it must be the thermostat which you can find behind the main control knob and he is going to get me an estimate for that! I think I'll get a second opinion though LOL. Good luck!!
Ellen
December 2009