Using hot water is a popular DIY method to unclog a toilet without a plunger, as the heat helps break down organic waste and toilet paper. However, it must be done carefully to avoid damaging your plumbing.
Your toilet is made of porcelain. While porcelain is tough, it has terrible thermal shock resistance. Pouring boiling water (212°F) into a cold toilet creates sudden expansion. This causes the porcelain to crack violently—sometimes instantly, sometimes an hour later.
A cracked toilet bowl means water leaking into your floor joists and a full toilet replacement. A $200 plumber visit is cheaper than new subflooring.
