Glock 17 firing full auto?

[simon]

Probably been asked 100 times, but can anyone tell me why my Glock 17 have decided to fire full auto?
I have 3 different makes that this has only started to happen to this month.
I'm using the same ultra air gas as before and the mags are the same.
Has something worn in the mech? I also have a Glock 18c and I know that a part can break so the semi stops working, but thought this was a different hammer mech in the 18.
Any help please?
Thanks.