ok, i've had my slow cooker for ages and used it successfully loads of times. well last night i decided to make and enormous pork cassarole (so i can freeze some for later date). filled it almost to the top whereas normally it's only about half full. just wondered, does it take longer to cook the more there is in it?? i put it in at 7pm last night expecting it to be ready by now and the carrotts and potatoes are still hard. normally it's well ready after 10 hours. what have i done wrong???