Hello Steve I clean ovens, its hard work, you must make sure you thoroughly clean the whole of the inside. Using the strongest cleaner you can get, with a metal scourer, a lot of elbow grease, you can do the job. Make sure you only apply the cleaner to the stainless steel and enameled surfaces, NOT plastic, aluminium or powder coated surfaces. Or you can pay around £35+VAT to have it cleaned by someone with a dip tank, industrial strength chemicals and get as good as new oven. Mick