Water Heater Leaking From an Outside Pipe
On this page (6 sections)
The Short Answer: A wet pipe on the outside of a water heater usually means a connection that can be repaired, not a failed tank. Common sources are the connectors at the top, the relief valve and its discharge pipe, the drain valve, or condensate on high-efficiency models. Dry everything and watch where water first appears. Only water from inside the jacket, with every fitting dry, points to the tank.
Find which pipe it is
| Where the water is | Likely source | Urgency |
|---|---|---|
| Hot or cold connection on top of the tank | Loose or corroded connector, nipple, or union | Repair soon |
| Discharge pipe running down the side from the relief valve | Valve opening because of high pressure or temperature, or a worn valve | Find out why; never cap it |
| Valve near the bottom with a hose thread | Drain valve weeping | Minor repair |
| Small plastic tube or pipe on a high-efficiency unit | Condensate, which is normal when draining properly | Check the drain line |
| Metal vent pipe above the heater | Condensation or rain in the vent | See water heater vent pipe leaking |
| Water seeping from under the jacket, all fittings dry | Tank failure | Replace |
A. O. Smith’s bulletin on puddles around a heater (opens in a new tab) walks through the same sources, and its condensation bulletin (opens in a new tab) explains why a gas tank can drip from condensation, especially when filled with cold water.
What you can check safely
- Dry everything with paper towels: each connection on top, the relief valve and its pipe, the drain valve, and the floor.
- Wait and look. Check every few minutes for the first new drops. Water runs down pipes and along the jacket, so the lowest wet point is rarely the source.
- Note the timing. A relief valve that drips after the burner or elements run points to pressure from thermal expansion. A drip that happens all the time is more likely a fitting.
- If the leak is active, close the cold-water valve above the heater and turn off the gas or the breaker.
Never cap, plug, or reduce the relief valve discharge pipe. It is the tank’s protection against overpressure.
Relief valve discharge
A relief valve that drips during or after heating often means pressure is rising as the water expands. That’s common where there is a check valve or pressure-reducing valve on the main supply and the expansion tank is missing or waterlogged. A. O. Smith’s thermal expansion bulletin (opens in a new tab) explains the cause. See water heater expansion tank full of water and why does my hot water heater overflow keep discharging water.
What the plumber will check
A plumber measures the household water pressure and checks for pressure rising during heating. They test the expansion tank and inspect the relief valve. At the top of the tank they look at the connectors and dielectric nipples for corrosion, and tighten or replace them with support so the tank fitting doesn’t twist. They will also confirm the relief valve’s discharge pipe is the right size and ends where water can be seen safely.
Repair or replace
Connectors, nipples, unions, drain valves, relief valves, and expansion tanks are all repairs. A tank leaking through its shell is a replacement; see why water leaking from the bottom of the water tank.
Frequently Asked Questions
Q: Is it normal for the relief valve pipe to drip a little? A: An occasional drip usually means pressure is rising during heating, which should be corrected. A valve that keeps dripping after the pressure is fixed may be worn and need replacing.
Q: Can I keep using hot water while the outside pipe drips? A: If it is a slow drip from a fitting, usually yes until it’s repaired. If the relief valve is discharging hot water or the drip is getting worse, turn off the heater and close the cold-water valve.
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 15: condensation (opens in a new tab)Why combustion condensate can resemble a tank leak; not a diagnosis of another manufacturer’s model.
- 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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