What causes a toilet to leak from the base when flushing?

A toilet leaking from the base when flushing is most often caused by a failed wax ring seal between the toilet and the floor flange. That seal commonly gives out after years of compression or when the toilet can rock even a little during use. We handle this repair routinely for homes around Gresham, and a proper reset with a new wax ring, secure closet bolts, and a flange check stops the leak at the source.

Look for these typical causes:

• Loose or corroded closet bolts that no longer compress the seal
• A damaged or out-of-level toilet flange that prevents a tight seal
• A hard clog that forces flush water past a weakened seal

Shut off the toilet’s supply valve and avoid flushing again until a plumber can reseal and test it.

Updated: 2026-03-11

Need help in Gresham, OR? Call (503) 404-3527 or book online. "Sky did a great job repairing my toilet!" — Will Ball