Water Heater Won't Stop Draining
On this page (7 sections)
The Short Answer: A tank that keeps draining is still being fed by the cold-water supply through a valve that is open or will not seal: usually the drain valve at the bottom, or the temperature and pressure relief valve. Close the cold-water inlet valve, turn off the gas or electric supply, and see whether the flow stops. If the drain valve will not close, a plumber can replace it.
Stop the water first
- Close the cold-water inlet valve on the pipe feeding the heater. If it will not close, shut off the main water valve to the house.
- Turn off the energy. Electric: switch off the breaker. Gas: turn the gas control to OFF. An electric element that runs in a draining tank will burn out.
- Watch the flow. Once the inlet is closed, the flow should slow and stop as the tank stops refilling. If it keeps going until the tank is empty, that is just stored water leaving.
Which valve is running?
| Where water is coming from | What it is | Likely fix |
|---|---|---|
| Drain valve at the bottom (hose thread, plastic or brass) | Valve left open, or sediment holding it open, or a cracked plastic valve | Close it; if it won’t seal, replace the valve |
| Relief valve pipe (brass valve near the top, pipe running down) | Relief valve opening or stuck open | See below |
| A pipe connection or the tank body | Leak, not draining | See leaking from the bottom |
| Hose on the drain valve with its end in a lower sink or drain | Siphoning through a partly open valve | Close the valve; lift the hose end |
A drain valve that won’t close
After a flush, sediment often lodges in the valve seat, so the handle turns closed but water keeps trickling. Factory plastic drain valves are prone to this and can crack if forced. With the cold inlet closed, gently opening and closing the valve once may flush the grit out. If it still drips, a cap on the hose threads can hold it temporarily until a plumber replaces the valve with a brass one. Do not overtighten the valve or use a wrench on the plastic body; if the tank fitting turns, the tank can be damaged. See plastic drain valve dripping.
A relief valve that won’t stop
The temperature and pressure relief valve opens on high pressure or high temperature. If it keeps discharging, the cause may be high house water pressure, a missing or failed expansion tank, an overheating heater, or a valve that did not reseat after it was tested. Never cap or plug the relief valve or its pipe. See relief valve stuck open and overflow keeps discharging.
Before turning the heater back on
The tank must be completely full again. Close the drain valve, open the cold-water inlet, and run a hot faucet until water flows steadily without air. Only then restore power or relight following the label. Powering an electric heater with air in the top of the tank burns out the upper element; see turned on without water.
What the plumber will check
They will replace a drain valve that does not seal, check house water pressure and the expansion tank, test whether the relief valve is responding to pressure or temperature, and check the heater’s thermostat or gas control if it is overheating.
Frequently Asked Questions
Q: Why does water still come out after I closed the cold inlet? A: The tank still holds its stored water, which will keep draining through any open valve until the tank is empty. If water keeps coming much longer than the tank’s capacity, the inlet valve is not fully closed.
Q: Can I leave a hose on the drain valve with a cap? A: A hose cap is a short-term measure. A drain valve that will not seal should be replaced, because sediment or a crack can let it start leaking again.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- A. O. Smith technical bulletin 51: puddles around a heater (opens in a new tab)Common water-leak sources and the distinction between fittings and a failed tank.
- A. O. Smith technical bulletin 45: thermal expansion (opens in a new tab)Background on pressure rise in a closed water system. Pressure testing and repairs are professional work.
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