Water Heater Sounds Like Running Water
On this page (6 sections)
The Short Answer: A running-water sound with every faucet closed means water is actually moving somewhere. The usual sources are the temperature and pressure relief valve discharging, a leak at a fitting or the tank, a recirculation pump, or a fixture in the house that is quietly running and making the heater refill. Find the wet pipe or the open fixture before assuming the heater is at fault.
Narrow it down
| What you notice | Likely source | How urgent |
|---|---|---|
| Relief-valve discharge pipe is wet or dripping into the pan or drain | Relief valve opening on high pressure or temperature, or a worn valve | Same day if dripping; a steady stream is urgent |
| Water at the base or inside the drain pan, discharge pipe dry | Fitting, drain valve, or tank leak | Find the source today |
| Sound continues, heater is dry, a recirculation pump is installed | Recirculation pump running on a timer or demand | Normal if scheduled |
| Gas tankless fires with no tap open | Hidden draw: toilet fill valve, outdoor hose, recirculation | Check fixtures |
| Condensing heater, cool trickle in white plastic drain line while firing | Normal condensate | Normal if it reaches a drain |
| Sound only while heating, popping or rumbling | Sediment, not running water | See sounds like rocks |
The relief valve is the most common cause
The temperature and pressure (T&P) relief valve opens when tank pressure or temperature gets too high, and the discharge sounds just like a tap running into a drain or pan. The usual reasons are high house water pressure, thermal expansion in a home with a check valve or pressure-reducing valve and no working expansion tank, or a valve that did not reseat after it was tested.
A steady stream from the discharge pipe while the heater is running can also mean the water is overheating. Turn the heater off (gas control to OFF, or the breaker for an electric heater) and call a plumber. Never cap or plug the discharge pipe. More detail: overflow keeps discharging and relief valve stuck open.
What you can check safely
- Dry the relief-valve discharge pipe, the drain valve, the pipe connections on top, and the floor with paper towels. Wait a few minutes and see which one gets wet again.
- Walk the house: toilets that run or refill on their own, a dripping shower, an outdoor hose bib, an irrigation line.
- If you have a recirculation pump, see whether the sound stops when the pump is off or outside its scheduled hours.
- Read your water pressure with an inexpensive gauge on an outdoor hose bib. Plumbing codes generally call for a pressure-reducing valve when pressure exceeds 80 psi.
- If water is spreading, close the cold-water inlet valve to the heater and turn off the gas control or breaker.
What the plumber will check
Static house pressure, the condition and precharge of the expansion tank, whether the relief valve opens because of pressure or because the heater is overheating, and every fitting on the tank. On a tankless unit, they will also look at whether the flow sensor sees a constant small draw and whether the recirculation controls are set correctly.
Repair or replace
A dripping relief valve, a bad fitting, a failed expansion tank, or a running toilet are repairs. Water coming from the tank itself, with every fitting dry, means the tank has failed and the heater needs replacing. If the heater is leaking but you still need water in the meantime, see can you still use water if the water heater is leaking.
Frequently Asked Questions
Q: Is it normal for a tank heater to make a filling sound? A: Only right after hot water is used, when cold water flows in to replace it. A tank does not keep filling with every tap closed. If the sound continues, something is drawing or leaking water.
Q: The relief pipe runs into a drain, so I can’t see it dripping. How do I check? A: Feel the discharge pipe a short way down from the valve. A warm pipe, or one with condensation on a dry day, suggests the valve has been releasing water. You can also listen at the pipe.
Q: Could a tankless water heater be leaking even if I don’t see water? A: Yes. Water can run down inside the cabinet or into a wall. Look under the unit and at the bottom of the cabinet, and if you suspect an internal leak, close the service valves and call for service.
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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