There's a point at which the buyer and seller no longer have a relationship - the seller has the money, the buyer has the deed, and they go their separate ways. That time is "closing day," unless agreed otherwise, and it's at that time when the buyer has to give up looking for someone to blame, and just get the problem fixed.
All the best,
Then see if it was mentioned anywhere in your inspection.
If it wasn't discovered during your inspection....and there are no signs that it was an old problem that the sellers tried to cover up - I am afraid it's your responsibility.
Welcome to the world of home ownership..........you never know waht might break next!
hope that helps
Dave & Lisa