Combi cooking

[momac]

I have been using a combination cooker now for a couple of years (Panasonic) I usually do my main cooking on convection..three times this last couple of weeks it has burnt food to a cinder long before the cooking time is up...it seems to burn all at once,one minute everythings fine then all of a sudden I smell the burning.has anyone else had this problem..am getting a bit cheesed off with it now. thank you.