Water Heater Leaking: Causes and What to Do Now
A leaking water heater needs two things from you right away: shut off its power or gas, and close the cold water supply valve on top so the tank stops refilling. Then find where the water is coming from. A leak from a valve or fitting is usually a cheap repair, while water from the tank itself means the heater has to be replaced.
What to do right now
- Cut the energy. Breaker off for electric; gas control knob to off for gas.
- Stop the water. Close the cold supply valve on the pipe going into the top of the heater. The rest of the house keeps cold water.
- Protect the floor. Towels, a bucket, or a wet vac. Move boxes and anything electrical.
- If the tank itself is leaking, drain it. Connect a garden hose to the drain valve and run it to a floor drain or outside, then open a hot tap upstairs to let air in. Our drain guide has the full routine.
Is a leaking water heater dangerous? The leak itself is usually just water damage. The danger comes from what's near it: scalding water, live wiring, gas controls, and a relief valve that may be opening because pressure or temperature is too high.
Where is it leaking from?
Dry the heater and the floor, then watch or use dry paper towels to find the first wet spot. Water runs down, so start at the top.
| Where you see water | Likely cause | Usual fix |
|---|---|---|
| Pipe connections on top | Loose or corroded fitting | Tighten or replace the fitting |
| T&P valve or its discharge pipe | High pressure, thermal expansion or a worn valve | Check pressure, add or recharge an expansion tank, replace the valve |
| Element covers (electric) | Failed element gasket | Tighten the element or replace the gasket |
| Drain valve at the bottom | Valve not fully closed or faulty | Close, flush, cap or replace |
| Base of the tank, under the jacket | Corroded tank | Replace the heater |
| Under a gas burner, only on cold starts | Condensation | Usually stops when the tank heats |
The detailed guides: leaking from the top, leaking from the bottom, drain valve leaking and relief valve leaking.
The common causes, explained
Fittings and connections
The water lines on top flex and heat up every day. Threaded joints loosen, and the fittings where copper meets the steel tank corrode. HomeGuide notes that leaks from a fitting, bolt or drain valve may only need tightening. Corroded nipples or connectors need replacing.
The relief valve and its overflow pipe
The "overflow pipe" people see dripping is the discharge pipe from the T&P valve (temperature and pressure relief valve). It's supposed to run down the side and end near the floor. A.O. Smith's manual says it should terminate no more than six inches above a floor drain or outside, and must never drain into the drain pan.
Water from that pipe means the valve opened. A.O. Smith points to high pressure or thermal expansion. Check your water pressure with a gauge on a hose bib; A.O. Smith recommends 50 to 60 psi and no more than 80 psi. In a closed system, heated water expands with nowhere to go and pressure climbs. That's what a thermal expansion tank is for. Never cap or plug the relief valve or its pipe.
Element gaskets
On electric tanks, each element seals against the tank with a gasket. When one fails, water seeps behind the access cover and soaks the insulation. With the power off, A.O. Smith's manual says to tighten the element until the leak stops, and replace the gasket if it's damaged.
The drain valve
Near the bottom, the drain valve may not be fully closed or may have worn out. Sediment in the seat can keep it from sealing.
A corroded tank
Steel tanks are protected by a glass lining and an anode rod. Once the anode is used up, the tank starts to rust from inside. When it rusts through, there's no repair. A.O. Smith says a corroded, leaking tank usually means the whole heater needs to be replaced.
Drip trays and drain pans
A drain pan under the heater catches small leaks and condensation before they reach the floor. A.O. Smith's manual calls for a pan at least 2 inches wider than the heater, with water depth limited to 1-3/4 inches. A pan with a drain line to a floor drain is better than one that just fills up. See water heater drain pans.
When to call a plumber, and what it costs
Call a plumber if the tank is leaking, the relief valve is discharging hot water, your pressure is over 80 psi, or a fitting is too corroded to turn. HomeGuide's figures:
| Repair | Typical cost |
|---|---|
| Leak repair, depending on the source | $100 to $1,000 |
| Pressure relief valve replacement | $50 to $300 |
| Expansion tank replacement | $300 to $800 |
| Replacing a leaking tank heater | $600 to $1,800 |
Expect a service call fee of $50 to $200 in many areas. If the heater is old and the quote is high, compare it with water heater installation cost before you agree to a repair.
FAQ
Why is my hot water heater leaking?
The usual causes are a loose fitting, a relief valve opening because of high pressure or thermal expansion, a failed element gasket, a drain valve that won't seal, or a corroded tank. Where the water first appears tells you which. Start at the top and work down.
Is a leaking water heater dangerous?
It can be. A relief valve that keeps opening is warning you about pressure or temperature. Water near wiring is a shock risk, and a gas heater near standing water needs a pro to check the controls.
How long will a water heater last once it starts leaking?
If the leak is from a valve or fitting, the heater can run for years after a repair. If the tank itself is leaking, there's no safe timeline; it can go from a seep to a flood with no warning. Replace it soon.
How do I drain my water heater?
Turn off the power or gas, close the cold supply valve, connect a hose to the drain valve and run it to a drain or outside. Open a hot tap to let air in, then open the drain valve. Our drain guide has the details.
What if the water heater is leaking from the inside?
Water from under the jacket or the base usually means the inner tank has corroded through. Shut off the water and energy, drain the tank, and plan a replacement. Our water heater replacement cost page shows what to budget.
Sources
- A. O. SmithResidential Electronic Thermostat Electric Water Heater: Installation Instructions and Use & Care Guide (opens in a new tab)
- A. O. Smith / State Water HeatersResidential Hybrid Electric Heat Pump Water Heater Service Handbook (opens in a new tab)
- A. O. SmithWater Heater Not Working? Troubleshooting Guide (opens in a new tab)
- HomeGuideWater Heater Repair Cost (opens in a new tab)