This is common in hard-water areas like San Diego, where sediment builds up fastest, often in heaters that have never been flushed.
Safety first
Water in a tank can be scalding. Turn the heater off and let it cool for a few hours before draining, wear thick gloves and eye protection, and keep hands clear of the drain valve discharge.
Cause 1: no air getting in
A tank needs air to replace the water draining out. Manufacturer instructions call for opening a nearby hot-water faucet before opening the drain valve. If you skipped that step, open a hot tap and try again.
Cause 2: sediment clogging the drain valve
A.O. Smith notes that sediment can clog the drain valve and stop the tank from draining, and advises calling a plumber or service technician. Rheem says the same if the valve will not open or is leaking.
What not to do
- Do not force or hammer a stuck valve; a broken drain valve on a full tank is a flood.
- Do not turn the power or gas back on with a partly drained tank.
General information, not professional or legal advice; follow your manufacturer's manual, and your installer and local permit office have the final word. Sources:A.O. Smith, How to drain a water heater; Rheem, How often to flush your water heater; A.O. Smith residential electric water heater manual (185762); Bradford White installation & operating manual.
Water Heater Repair in San Diego →