Hit the pressure release valve. Next time this happens look around and find the button or lever or old fashioned knife switch labeled "pressure release valve"

Hit the pressure release valve. Next time this happens look around and find the button or lever or old fashioned knife switch labeled "pressure release valve" or something like that and push/pull/flip/throw it. (I'm seriously. The brain works like that. Draw a door on the wall and open it and walk through.)