If you have tried heat for two hours with zero success; if you have cast iron pipes; or if you cannot find the location of the freeze, call a plumber. They have steam machines and electric thawing equipment designed specifically for this. It will cost you a few hundred dollars, but that is significantly cheaper than replacing a burst pipe and remediating sewage damage.
Recognizing the early symptoms of a frozen drain can save you from a major sewage backup:
: Even a tiny "trickle" leak from a faucet can gradually freeze inside a waste pipe, eventually creating a solid ice dam [5.1, 21].
: Air trapped behind an ice blockage can cause "glugging" or banging as water tries to move past [8, 16].
You flush the toilet. The water rises. You wait. And wait. Instead of the satisfying swoosh of departure, you are met with a slow, ominous backflow.
: If waste cannot travel away from the home, it remains stuck in the system, causing smells to back up into the bathroom or kitchen [9, 16].
