It’ll prob be 3 secs then resetting – E10 is no inverter output – If he’s played around with the door , perhaps the door switches aren’t being made now ? Was it working before he replaced the glass ?
On the odd occasion , these have also been known to blow the 8/10a internal fuse if the door’s opened during use . The door switches must operate simaltaneously so a ‘wonky’ door can cause probs.
I always advise customers to pause cooking before opening the door if they need to check food.