How To Shut Off a Leaking Water Heater
Three things in order: close the cold water inlet valve at the top of the tank, cut the energy to it, then drain it if you can do so safely. Doing them out of order can damage the heater or create a hazard.
What to do right now
Do these first. None of them need tools or plumbing knowledge, and they limit what this ends up costing you.
Stop and get out if any of these are true
If you smell gas anywhere near the water heater, leave the building immediately. Do not touch any switch, do not use a phone indoors, and call the gas utility from outside before you call a plumber.
- Close the cold inlet valve firstAt the top of the tank on the incoming pipe, usually a lever or a round handle. Clockwise for a round handle, or a quarter turn for a lever. This stops the tank refilling as it leaks.
- Cut the energy secondElectric: find its breaker in the panel and switch it off. The elements must never run in a tank that is emptying, because they burn out in seconds and can be a fire risk. Gas: turn the control dial on the front to off, or to pilot.
- Drain it only if you can do it safelyA hose on the drain valve at the base, run to a floor drain or outside. The water is scalding hot unless the tank has been off for hours, so this is optional and it is not worth burning yourself for.
Does this need a plumber tonight?
- Any smell of gas, in which case leave the building first
- Water reaching electrical equipment
- A relief valve discharging steam or very hot water
- Water you cannot stop with the inlet valve closed
- A tank isolated at the inlet with the leak contained
- A small drip at a fitting
Why the order matters
Cutting the water first means the tank stops refilling immediately. Cutting the energy first while water keeps arriving simply gives you a full tank that is still leaking.
The electric case is the one where order genuinely matters for safety. Elements exposed to air in a partially drained tank fail almost instantly and can create a fire risk. Switching the breaker off before draining prevents that entirely.
On gas the risk profile is different but the sequence is the same. Turn the control to off or pilot rather than touching the gas supply line.
What not to do
Do not cap the relief valve, do not drain a hot tank in a hurry, and do not relight a gas heater that has been sitting in standing water.
The temperature and pressure relief valve is a safety device. If it is discharging, something is wrong with pressure or temperature and blocking it removes the protection rather than solving the problem.
A gas control valve or a burner assembly that has been submerged should be assessed before the heater is used again. Water and gas controls are not a combination to take chances with.
When to call rather than continue
[PLACEHOLDER: PRICING] Pending from the client.
If you smell gas, if water has reached electrical equipment, or if the inlet valve will not close, stop and call. Those are the three cases where continuing on your own is not worth it.
Questions people ask about this
Where is the cold inlet valve?
At the top of the tank, on the pipe carrying cold water in. It is usually marked blue or is simply the pipe that stays cold. If there is no valve there, use the main house shutoff instead.
Should I drain it?
Only if the water has cooled and you have somewhere for it to go. It is not essential and a full tank that is isolated and switched off is stable.
Can I turn it back on afterwards?
Not until the leak is identified. An electric heater must be full before its breaker goes back on, or the elements burn out immediately.
If that is not quite what you have
Not sure how urgent this is?
Describe what you can see and hear. We will tell you whether it needs someone tonight, and what to do in the meantime either way.
Or send it over
Four things and a photo.