@DarkestPenguin There's an open bug thread here that might be appropriate for your problem, on Page 1 there's a list of other similar bug reports too that might also apply to you.
It can also happen just because the skill is too low if they are new Sims so I always get them to raise the cooking skill with Fruit Salad and Garden Salad first and some Cooking Channel too before using equipment but if it's still happening with frequency then that could be a bug.
Good luck.
https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-Constant-Fires-Reason-unknown/td-p/9636831