LJDUK Unfortunately it keeps dripping/releasing vapour. Initially I just thought it was due to cold weather /cooler kitchen but the drip tray is filling up.
It’s sounds like you need to replace the vacuum breaker, unless you can remove and clean it, or replace an O ring in it….I have not taken that type apart to know if they can be cleaned or the O ring replaced. It’s an easy enough job.
Ideally take the lid of and identify which fitting it is…one is a safety valve, the other is a vacuum breaker and they look similar, both have tubes on them…see which one it is, take a photo and identify it…then post the image on here.
If it does it as soon as the machine reaches 100, then it’s more likely to be the vacuum breaker….but both vent into the drip tray.