After having my old fusebox replaced by a modern (Wylex) box my Hotpoint 6170 fan oven switches off sometimes when in use (after between 5 and 15 minutes). Resetting the RCBO (residual current device) switch restores the supply. The oven is on its own circuit so other devices are not involved. Electrician says it’s a fault in the oven. What is this likely to be in a 35 year old oven? 🙁