Water Heater Leaking From the Bottom

Find the source first

Most bottom leaks aren't coming from the bottom. Water follows the outside of the tank and collects where it can't go any lower. Dry the heater and the floor, then check these spots with a dry paper towel, top to bottom:

1. The pipe connections and relief valve on top or near the top.
2. The relief valve discharge pipe, which runs down the side and ends near the floor.
3. The upper and lower element covers on an electric heater.
4. The drain valve near the bottom.
5. The burner area and the base of the tank.

Our page on a water heater leaking from the top covers the upper sources.

Likely causes

1. 1

   Cause 1: The drain valve

   The drain valve is a common bottom leak, and the easiest to fix. A.O. Smith says the valve may not be fully closed or may be faulty. Close it firmly, flush a few seconds of water through it to clear sediment, and cap the outlet. Full steps are on water heater drain valve leaking.

2. 2

   Cause 2: The relief valve discharge pipe

   The pipe from the T&P valve (temperature and pressure relief valve) is supposed to end close to the floor. A.O. Smith's manual says it should terminate no more than six inches above a floor drain or outside the building. If water is coming out of that pipe, the leak isn't at the bottom at all. The relief valve is opening because of high pressure or thermal expansion, or it has worn out. See water heater relief valve leaking.

3. 3

   Cause 3: A lower element gasket (electric)

   A.O. Smith notes that leaks can occur around the heating elements if the gaskets fail. Turn the power off, remove the lower access panel and look for wet insulation or rust around the element. The manual says to tighten the element until the leak stops, and to replace the gasket if it's damaged.

4. 4

   Cause 4: Condensation

   A gas heater refilled with cold water can sweat inside the combustion chamber, and drips can land under the burner. It looks like a leak but stops once the tank is fully hot. If the puddle dries up within a couple of hours and doesn't come back, this was probably it. The manual recommends a drain pan to catch condensation and leaks.

5. 5

   Cause 5: A leaking tank

   If the water comes from the base of the tank, from under the jacket, or from the burner area with no other source, the inner tank has corroded through. A.O. Smith says that once the tank corrodes and leaks, the entire water heater usually needs to be replaced. Rust-colored water at the base and a tank past its expected life both point the same way. HomeGuide puts standard tank lifespans at 8 to 12 years.

Tankless water heater leaking from the bottom

A tankless unit has no tank to rust out, so a bottom leak is usually a fitting, the pressure relief valve, or, on condensing models, the condensate line. Check the service valves and connections under the unit and the condensate drain. If water is coming from inside the cabinet, turn the unit off and call a technician; internal heat exchanger leaks are not a homeowner fix. Our tankless repair page has more.

What to do right now

1. Turn off power or gas to the heater.
2. Close the cold water valve on top of the heater. The rest of the house keeps its cold water.
3. Put a pan or towels under the leak, and move anything that can't get wet.
4. If the tank itself is leaking, drain it to stop the leak and protect the floor. Connect a hose to the drain valve and run it to a floor drain or outside.

A drain pan helps next time. A.O. Smith's manual says the pan should be at least 2 inches wider than the heater.

When to call a plumber, and what it costs

If the leak is from the tank, call a plumber about a replacement. HomeGuide says leaking tanks typically require replacing the water heater for $600 to $1,800. For a fitting, valve or gasket, leak repair runs $100 to $1,000 depending on the source, and a relief valve replacement costs $50 to $300.

Compare repair and replacement on water heater installation cost before you approve work on an old tank.