How clean is your oven?

Well until this happened last night our oven was really quite clean.  Its a super, duper Miele oven with all sorts of bells and whistles.  Granted it is around 7 years old but even so you wouldn't expect it to go on fire now would you!  We had just put some chips in the oven at 200 degs. and suddenly sparks started to shoot out of the grill on the back wall and fly everywhere inside.  Lots of white smoke too and the temperature started to shoot up rapidly to around 280 degs.  Not too good at all...  So I managed to switch it off and rescue the chips!  I spoke to some very nice people at Miele this morning and they have arranged for one of their own engineers to come up next Friday, 4th December!  Despite protests on the home front, I am leaving the inside exactly as it is to show the engineer when he/she arrives :)