Cleaning Bosch HBN 13N5.OB

Nearly a year ago we moved into a brand new house with a HBN 13N5.OB Bosch oven. We are having real problems keeping it clean – there is this black/brown sticky substance all over the bottom of the oven which we cannot clean off. To be honest we don’t do an awful lot of cooking in it, certainly we haven’t allowed foods cooking to spill on the oven floor and not wipe it up. Does anyone have the same problem or have any advice on cleaning it? Maybe my oven has a fault as my neighbours don’t seem to have the same problem.

Thanks – Tam