Water Heater Leaking: What to Do First

First: make it safe and stop the water

1. If you smell gas (rotten-egg odor) near a gas heater: leave the house, don't touch switches, and call 911 or your gas utility from outside. Nothing else matters until that's cleared.
2. Turn off the power or gas to the unit. Electric: flip the water heater breaker. Gas: turn the control knob on the unit to "pilot" or off. A heating tank with a leak can be damaged — or dangerous — if it keeps firing while losing water.
3. Shut off the cold water supply to the heater. There's a valve on the cold line into the top of the tank; turn it off and the leak slows to what the tank still holds. If that valve is stuck or missing, use the house's main shut-off.
4. Protect the area. Move what's stored around the unit, get towels down, and take a photo of where the water is coming from before you mop — for the pro and, if it comes to it, for insurance.

Once the supply is off, the clock slows down. Now find the source.

Where the leak is coming from decides everything

Leaking from the top — inlet/outlet fittings. Water around the pipes where they enter the top of the tank, or running down from a fitting, is usually a loosened or corroded fitting — the good-news leak, since connections can be repaired without replacing the tank. Dry everything thoroughly first; water from a top leak runs down and pools at the base, masquerading as a tank failure.

Leaking from the T&P relief valve (side, near the top). The temperature-and-pressure relief valve has a discharge pipe running down the side of the tank. Occasional drips from that pipe can mean the valve is doing its job against excess pressure — but a valve that drips constantly is either failing or warning you about a pressure/temperature problem. The valve itself is replaceable; the underlying cause still needs a diagnosis. Never cap or plug a T&P discharge pipe, ever.

Leaking from the drain valve (near the bottom, hose thread). The small faucet-like valve used to drain the tank sometimes weeps, especially after a flush. Often it's debris in the seat, and the valve can be replaced — a repair, not a replacement, as long as the tank itself is sound.

Leaking from the bottom of the tank itself. This is the bad one. If water is seeping from the tank body — the base pan is wet but every valve and fitting above it is dry — the steel tank has corroded through from the inside. There is no repair for a failed tank; patch products don't change that. The unit needs replacement, and the question becomes how fast: a seeping tank can let go completely, and 40–50 gallons plus the incoming line is a flood, not a puddle. Keep the supply off and treat it as urgent.

How fast does this have to happen?

A leaking valve or fitting, with the supply controlled, can usually be a same-day or next-day repair. A leaking tank is different — it has already failed; what remains is scheduling its exit before it floods. In a Windsor winter, pros prioritize tank replacements because losing hot water in January is miserable — and a like-for-like swap is typically a few hours' work once the unit is on site.

Two Colorado specifics: replacement generally requires a permit and inspection (gas, venting, pressure safety) — the installing pro should pull it, and a no-permit quote is a red flag. And confirm haul-away is included; a proper install removes the old unit.

How long can you run a leaking water heater?

A valve or fitting leak, water contained, buys a little time — days, not weeks, with the puddle watched. If the tank body is leaking, the answer is: don't. Every heating cycle stresses the failing steel. Shut it down, keep the water off to it, and replace it.

Common questions

Standing in water by your water heater?

Shut off the supply valve, then call (970) 839-0039 — you will be matched with an available local pro. If it's a valve, it's a repair. If it's the tank, you'll get replacement options and a price you approve before work begins, permit and haul-away included.

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