Yeh I agree with them,check your tank I see split ones all the time. All the water housings give up eventually and are normally brittle to touch or break away where the O rings sit. Refill it with water and put the cap on,run it for 5 mins and check around the area you saw the steam. It should be fairly obvious where the water is coming out if it went pop. Don't run it for too long though,you don't want to cause any damage,and there is a couple of bleed screws to let the air out also. If you aren't sure best get someone with some knowledge to sort it for you.
