Hotpoint oven SY86P Overheating- Not the temperature probe

Hi everyone,

Looking for some help with fixing a hotpoint SY86P oven. Since ~ April it’s been overheating to the point where it will enter self-cleaning mode and lock itself until it’s cooled down regardless of temperature set (just set it to 40° and it still got past 250 and locked itself).

Had a repairman come out and without even looking inside the oven he claimed it was the temp probe and that “it would be cheaper to buy a new oven, that he sells for £350”. We did not take him up on the offer.

Bought a replacement temperature probe though UKWhitegoods, just installed it and frustratingly the issue is still present. Is there anybody here who might have an idea what’s causing it? Wife and I are expecting a kid early next year and if we can avoid paying for a new oven it’s preferable!

edit for a bit more information as I’m taking a look

Cooling fan appears to be working. I’m not getting any error code but it gets to a point where the display just says HOT and locks the door until it cools down. Makes me think it’s a cooling issue but I can’t figure out what’s causing it.