Hair/grease buildup, venting issues, partial clogs deeper in pipes.

Unexplained water bills, mold smells, meter test (check if running when water is off

Shut off the main water valve, turn off the water heater, and call a 24/7 plumber.

Every 1–2 years for maintenance; more if you notice slow drainage.

Not recommended—they corrode pipes. Use baking soda/vinegar or call a pro.

8–12 years (tank) vs. 20+ years (tankless). Signs it’s failing: rust, leaks, noise.