Most Korean heaters have a button you are supposed to push when you leave the apartment.
I used this and still came home to gushing water after a 2 week vacation. My school was less than helpful to my panicked call about the flood (thankfully outside!) and said they wouldn't come to deal with it that night because it was so late. Thankfully I figured out how to turn the water off and bailed the excess down the gutter with a mixing bowl and turned the ondol off! (my sink/toilet still has water with no problem). The worse part was while I was doing that it took my coteacher a half hour to call me back and tell me no one was coming, sigh.
I think the fix on my end will be easy as it seems a joint cracked, not the actual pipe, but I'm afraid it leaked to the two floors below and caused damage ??? I was warned I might be liable for the damage because I went on vacation and wasn't here to supervise (and not because korean plumbing in the coldest province is completely inadequate and the pipes are in the process of rusting through naturally).
The guy is coming sometime today (no one has told me when of course) so I'll see the damage to my wallet and hot water soon enough.
Edit: I was right. It had nothing to do with me at all... the pipe was rusted through. It was literally dropping huge flakes of rust on my kitchen floor as the plumber took it out to his truck. Unfortunately I didn't get a picture but there's a big pile of rust outside on the stairs where he set it down. 100, 000 won my school/landlord won't pay for and a suddenly really warm ondol... it could've been worse.