Water Heater Leaking? What to Do First

Water around a water heater means one of two very different things: a repairable leak at a connection, or a failed tank. The first costs a fitting and an hour. The second means replacement, and there's no repair anyone can honestly sell you.

Find out which before you call anyone.

Where it is leaking from

A T&P valve discharging is often not a bad valve — it is doing its job because pressure is too high, frequently from thermal expansion on a closed system with no expansion tank. Never plug it.

What should you do first if a water heater leaks?

If water is spraying, the tank is visibly bulging, you hear it straining, or the relief valve is discharging steam — shut it down and stay clear.

Shutdown sequence:

1. Turn off the power or gas.
   • Electric: switch off the breaker for the water heater at the panel.
   • Gas: turn the gas control valve to OFF. Turn off the gas supply valve to the appliance if you can reach it safely.
   • Do this before draining. An electric element energised in an empty tank burns out immediately; a gas burner firing on an empty tank is worse.
2. Turn off the cold water supply — the valve on the cold inlet at the top of the heater. If it won't close, use the main shutoff.
3. Contain the water — towels, a wet vac, and move anything valuable out of the way.
4. Drain it if the leak is significant: attach a hose to the drain valve and run it to a floor drain or outside. The water is hot — let it cool first if you can, and open a hot tap somewhere in the house to let air in so it drains.

If you smell gas at any point: leave the house and call the gas utility or emergency services from outside. Don't operate switches.

Where is my water heater leaking from?

Dry everything completely, then watch. Water travels, so where it pools is often not where it comes from.

Check in this order:

1. Plumbing connections at the top. The hot and cold fittings. Corrosion or a slow drip here is common and repairable. Dielectric unions between dissimilar metals corrode over time.

2. The drain valve at the bottom. A frequent culprit, especially after a flush. Often just needs tightening; sometimes the valve itself has failed and needs replacing. Cheap either way.

3. The temperature and pressure relief (T&P) valve and its discharge pipe. If water is running from the discharge pipe, the valve is opening. That's covered below — it's a different problem from a leak.

4. The anode rod fitting at the top, if it's been serviced. See water heater anode rod.

5. Elements and gaskets on an electric heater. Element gaskets can fail and leak around the element flange — repairable.

6. Condensate, on a high-efficiency gas unit or a heat pump water heater. These produce condensate by design, and a blocked drain line backs it up. Not a tank failure. See heat pump water heater explained.

7. Something else entirely. A nearby pipe, a condensate line from an air handler, or a foundation issue. Check the surroundings before condemning the heater.

8. The tank itself. If everything above is dry and water is appearing at the base — especially rusty or discoloured water, with corrosion or staining visible on the tank body — the tank has failed.

Can a leaking water heater tank be repaired?

A steel tank is protected by a glass lining and a sacrificial anode rod. When the lining cracks and the anode is spent, the steel corrodes from the inside until it perforates.

There is no repair. Patching, sealing compounds and welding are not viable on a lined pressure vessel holding hot water. Anyone offering to repair a leaking tank is selling you a delay.

And it will get worse. A pinhole becomes a larger failure, and tanks can fail suddenly and release their entire contents. If your heater is in a finished basement or an upper floor, that's a serious water damage risk.

Plan for replacement now, not after the flood. Price it with the water heater replacement cost calculator.

What does a T&P valve leak mean?

The temperature and pressure relief valve is a safety device. It opens when water temperature or pressure exceeds its rating, preventing the tank from becoming a pressure vessel failure. Water discharging from its pipe means it's doing its job.

Never plug, cap, or restrict the T&P valve or its discharge pipe. Not with a cap, not with a valve, not with a threaded plug. This is one of the genuinely dangerous shortcuts in home plumbing.

Why it's discharging:

• Temperature too high. Check the thermostat setting — see water heater temperature setting.
• Thermal expansion in a closed system. With a backflow preventer or pressure-reducing valve on the supply, heated water has nowhere to expand to, so pressure rises. The fix is a properly sized, properly charged thermal expansion tank. A failed expansion tank produces exactly this symptom.
• High supply pressure. Measure it with a gauge on a hose bib; a pressure-reducing valve may be needed or may have failed.
• A failed valve. They corrode and can weep or stick. Replacement is straightforward — but only after ruling out the causes above, because a valve replaced without fixing high pressure will just do the same thing.

The discharge pipe must run to an approved location per code — typically terminating near the floor or outside, unthreaded at the end so it can't be capped.

Should you repair or replace a leaking water heater?

Repair when: a fitting, drain valve, element gasket, T&P valve or condensate line is leaking, and the heater is reasonably young. These are cheap fixes.

Replace when:

• The tank is leaking — no choice
• The unit is at or beyond typical service life. See how long does a water heater last
• Repairs are stacking up
• It's in a location where a failure would cause serious damage — replace proactively rather than waiting

A leaking heater is a decision point. Since you're paying for the installation labour either way, consider:

• A heat pump water heater, which uses considerably less energy than resistance electric — see heat pump water heater explained, and check the electrical and clearance requirements in heat pump water heater electrical requirements and heat pump water heater placement requirements
• Tankless, if the use pattern suits it — see tankless vs tank water heater
• Right-sizing — see what size water heater do I need
• Fuel switching — see gas vs electric water heater

Compare running costs with the electricity cost calculator and cost to run a water heater.

One venting caution: if you're removing a gas water heater that shares a chimney with another appliance, or leaving one alone in a flue previously shared with a furnace, the venting arrangement may need to change. See orphaned water heater venting.

Preventing the next one

• Flush annually to remove sediment, which accelerates corrosion and reduces efficiency — see how to flush a water heater
• Check the anode rod every few years and replace it when consumed. This is the single most effective thing you can do to extend tank life
• Install a drain pan with a drain line, especially where a failure would cause damage
• Consider a leak detector with an automatic shutoff valve
• Keep the T&P valve exercised per the manufacturer's guidance, and never cap it
• Check the expansion tank if you have one — a waterlogged one stops working silently
• Watch supply pressure

The bottom line

Shut off power or gas first, then water. Dry everything and find the actual source before calling anyone — fittings, the drain valve, the T&P discharge and condensate lines are all common and cheap, and water travels so the puddle location misleads. A leak from the tank body itself is replacement, full stop. And whatever else you do, never cap or restrict the T&P valve or its discharge pipe.

Price replacement with the water heater replacement cost calculator.