USA Expert Plumbing

Water heater leaking from the bottom: causes and what to do

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

A leak at the bottom of a water heater is usually the drain valve, the temperature and pressure relief valve draining down the tube, condensation, or water running down from a fitting above. If water is coming from the tank itself, the tank has corroded through and needs to be replaced.

In this guide
  1. First, stop more water from leaking
  2. The five common causes
  3. Drain valve leaks
  4. Relief valve discharge
  5. Condensation on gas heaters
  6. When the tank itself is leaking

Finding water under your water heater is stressful, but it does not always mean the tank is done. Several parts sit at or near the bottom of the unit, and some leaks start higher up and simply collect there.

The steps below help you find the source before you decide on a repair or a replacement.

Before you start: turn off the power at the breaker for an electric heater, or turn the gas control to the pilot or off position for a gas heater. Water in the tank can be hot enough to scald.

First, stop more water from leaking

  1. Turn off the power or gas as described above.
  2. Close the cold water shutoff valve on the pipe entering the top of the heater.
  3. Dry the area with towels so you can see where fresh water appears.
Diagram of a gas tank water heater with its main parts labeled
The main parts of a typical gas tank water heater. Electric models have heating elements and thermostats instead of a burner and gas valve.

The five common causes

CauseWhat you seeFixable?
Drain valveDrip from the valve near the bottom of the tankYes, tighten or replace
Relief valve (T&P)Water from the pipe running down the sideYes, but find out why it opened
CondensationSmall puddle, mostly when the burner runs on cold daysUsually no repair needed
Leak from aboveWater tracks down the jacket from pipes or fittingsYes, repair the fitting
Tank corrosionWater seeping from under the jacket or the baseNo, replace the heater

Drain valve leaks

The drain valve is the spigot near the bottom of the tank. Plastic valves on newer heaters often drip after a flush because sediment keeps them from sealing. Try closing it firmly by hand. If it still drips, a hose cap is a short-term fix, and replacing the valve with a brass one is a permanent one.

Relief valve discharge

The temperature and pressure relief valve opens when the tank gets too hot or the pressure climbs too high. Its discharge pipe ends a few inches above the floor, so a puddle here can look like a bottom leak. A valve that opens repeatedly usually means the thermostat is set too high or the house has high water pressure or no working expansion tank.

Do not cap or plug the relief valve pipe. The valve is a safety device that keeps the tank from over-pressurizing.

Condensation on gas heaters

When the tank fills with very cold water, moisture in the burner exhaust condenses on the cold tank and drips onto the burner area. It is most common in winter and after heavy hot water use. It should stop once the tank is fully heated.

When the tank itself is leaking

Water tanks are steel with a glass lining. Over time the lining cracks and the steel rusts through, usually from the inside out. Once that happens there is no reliable repair. Plan to replace the heater soon, and keep the water and power off until then if the leak is steady.

Common questions

Can I still use a water heater that is leaking from the bottom?

If the leak is from the drain valve or condensation, yes, once the cause is handled. If the tank itself is leaking, turn off the water and power and replace it, because the leak will only get worse.

How much does it cost to fix a leaking water heater?

A new drain valve or relief valve is an inexpensive part and a short job for a plumber. A leaking tank means replacing the whole heater.

Is a leaking water heater dangerous?

A slow leak mainly risks water damage. A relief valve that keeps opening is a warning sign of too much heat or pressure and should be checked promptly.

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