Water heater leaking from the bottom: what it means

If water is coming out of the tank itself near the bottom, the inner tank has most likely rusted through. There’s no repair for that. The heater needs to be replaced. But a lot of puddles under water heaters come from something else, like the drain valve, the relief valve pipe, or a fitting on top dripping down the side, so check before you assume the worst.

What to do right now

Whatever’s causing it, start here:

1. Turn off the heat. On an electric heater, switch off its breaker. On gas, turn the control knob to “off” or “pilot,” following the label on the unit.
2. Shut off the cold water going into the heater. There’s a valve on the cold line at the top. Turn it clockwise until it stops. If it won’t budge, or it’s the thing leaking, shut off the main instead. Here’s how to shut off the water to your house if you’re not sure where that is.
3. Open a hot water faucet somewhere in the house. That takes pressure off the tank and slows the leak.
4. Deal with the water. If there’s a drain pan, make sure its drain line is carrying water away. If there’s no pan, get towels down and move anything that shouldn’t get wet. Garage boxes are always the first casualty.

Is it the tank, or something else?

Dry everything off with a towel, then watch where the water shows up first. It can take a few minutes. Running your fingers along the pipes and fittings on top helps. Here’s what to rule out:

• The drain valve. That’s the spigot near the bottom where you’d hook up a hose to flush the tank. If it drips from the spout, it may just need to be closed snug or fitted with a hose cap. If it leaks around the body of the valve, the valve can usually be replaced without replacing the heater.
• The relief valve pipe. That’s the pipe running down the side of the tank from a valve near the top. More on that one below.
• The connections on top. A slow drip from the hot or cold line can run down under the outer jacket and come out at the bottom, where it looks exactly like a tank leak.
• Condensation. Gas heaters can sweat when the tank is full of cold water, like right after a lot of showers. The drips land near the burner and can look like a leak. If the puddle is small and goes away once the tank’s back up to temperature, that’s probably all it is.
• Something next door. Water heaters often share a closet or garage corner with the furnace or air handler, and a clogged AC condensate line can dump water on the same floor. North Alabama summers keep those lines busy. Look up and around before blaming the heater.

If you’ve ruled all of that out and the water is coming from under the tank, or seeping out through the jacket at the base, it’s the tank. Rust stains along the bottom seam are another sign.

What if it’s the relief valve?

The temperature and pressure relief valve, usually called the T&P valve, opens when the water gets too hot or the pressure gets too high. It’s there so the tank can’t build up enough pressure to burst. If its pipe is dripping, either the valve is doing its job because something else is wrong, or the valve itself is worn out.

The usual causes are household water pressure that’s too high, a thermal expansion tank that’s missing or failed, a thermostat that’s letting the water get too hot, or an old valve that won’t seal. Figuring out which one takes some testing, so this is a job for a plumber.

Never cap a relief valve. Don’t plug the pipe or screw anything onto the end to stop the drip, ever. That valve is the last safety device between a malfunctioning water heater and a tank that can rupture.

When the tank itself is leaking

Once the steel tank rusts through, it’s done. Tanks have a glass lining and a sacrificial anode rod to slow down corrosion, but the anode wears away over the years and then the tank starts rusting from the inside. A leak at the bottom seam is the classic sign. It usually starts slow and gets worse. Sometimes it lets go all at once.

No sealant or patch will fix it, so plan on a replacement and don’t put it off. On a garage slab, a slow drip is mostly a mess. In an upstairs closet it can bring down a ceiling. If you’ve got a few days to think it over, read tank or tankless before you pick the new one.

Why a drain pan and a leak alarm are worth having

A drain pan is a shallow tray under the heater with a line piped somewhere safe, like a floor drain or outside. It won’t hold back a burst tank, but it catches slow leaks and relief valve drips and sends them away from your floor. Codes commonly call for one where a leak could damage the house, like an attic or an upstairs closet. It’s a cheap part and worth having anywhere.

A leak alarm is even simpler. It’s a small battery-powered sensor that sits on the floor and beeps when it gets wet. Some send an alert to your phone. Set one in the pan and you’ll know about a leak the day it starts.

If you’ve got water on the floor and can’t tell where it’s coming from, shut the heater down the way we described above and give us a call.