Remember: Slow and steady heat wins this race. Patience prevents a costly pipe burst.
A frozen shower drain is a common winter nightmare. When the water in the trap or the horizontal pipe beneath the slab freezes, it expands and blocks the drain completely. If you run water, it will back up into the shower pan within seconds. how to fix a frozen shower drain
Never use a propane torch or an open flame to thaw a drain. You can melt plastic pipes, start a fire inside your wall, or generate steam that bursts the pipe. Remember: Slow and steady heat wins this race