Quick answer
To turn off a leaking water heater, close the cold-water valve on the pipe above the tank, then cut the energy: turn the gas control knob to OFF and close the gas shut-off, or switch off the double-pole breaker on an electric tank, or unplug a power-vent model. If the valve will not close, shut the house main. Then drain the tank through a hose to the floor drain.
The way to turn off a leaking water heater is three moves in a fixed order: water, then energy, then drain. Closing the cold-water supply stops the tank refilling, which turns an endless leak into one limited to the 150 to 230 litres already inside. Cutting the gas or power stops the burner or elements heating a tank that is emptying. Draining through a hose decides where that water goes, so the tank does not decide for you.
Step 1: close the cold-water shut-off above the tank
The shut-off sits on the cold inlet pipe on top of the tank, usually the right-hand pipe and the one that feels cool to the touch. Which way it turns depends on the valve type.
- Ball valve (lever handle): a quarter turn until the lever sits across the pipe. Lever in line with the pipe is open; lever at 90 degrees is closed.
- Gate valve (round wheel handle): turn clockwise until it stops, which can take six or more full turns. Do not force it; gate valves on older tanks seize, snap at the stem, or spin without sealing.
- Check that it worked: open a hot tap upstairs. The flow should fade to nothing in about a minute, and if it keeps running at full pressure the valve has not closed.
- Seized or leaking valve: go to the house main. On municipal water it is on the pipe where the service enters the basement, beside the water meter, most often on the front foundation wall.
- On a private well, as on rural lots around Kilbride, Lowville, Campbellville, Carlisle and rural Caledon: switch off the well pump breaker and close the valve after the pressure tank.
Step 2: shut off the gas or the power to the heater
- Gas tank: turn the knob on the gas control at the front of the tank to OFF. Then close the appliance shut-off valve on the gas pipe beside the heater with a quarter turn, so the handle sits across the pipe.
- Electric tank: switch off the double-pole breaker marked for the water heater, normally a 30-amp pair with the two handles tied together. An element left live in an emptying tank burns out, and water near live terminals is a shock hazard.
- Power-vent tank, the kind with a blower on top and a plastic vent pipe: set the control to OFF, then pull the plug from the wall outlet.
- Tankless unit: close the cold isolation valve beneath it and unplug it.
If you smell gas at any point, stop, leave the house and call Enbridge Gas from outside. If water has reached the burner compartment or the gas control, the heater stays off: a gas control that has been under water gets replaced, not relit.
Step 3: drain the tank through a hose to the floor drain
Draining is worth doing when the tank body itself is leaking, because closing the supply does not empty what is already in there. A 40-gallon tank holds about 150 litres and a 60-gallon tank about 230.
- Thread a garden hose onto the drain valve near the bottom of the tank and run the other end to the floor drain or sump pit. The hose end has to sit lower than the valve.
- Open a hot tap on an upper floor. This breaks the vacuum; without it the tank glugs and barely drains.
- Open the drain valve. Some have a small handle, others take a flat screwdriver.
- Keep hands and feet clear of the hose end, since stored water is around 60 °C and scalds in seconds.
- If the flow slows to a dribble, sediment has plugged the valve. Close it and leave the rest for the technician; do not remove the valve.
Which leaks can be repaired and which mean a new tank
Where the water is coming from decides the bill. Once the tank is off, look with a flashlight.
- Top fittings, flex connectors or the shut-off valve itself: repairable, inside the usual $150–$800 repair band.
- The relief valve discharge pipe or the drain valve: repairable. The causes are in why a relief valve drips.
- Rust trails down the jacket, water under the base, or water inside the burner compartment: the inner tank has failed. There is no patch for that, and a tank-for-tank replacement runs $1,200–$2,500 installed.
- A rental sticker on the jacket: the tank belongs to the rental company, so call the number on the sticker before paying anyone.
The rule we use at the door: a fitting or valve leak on a tank under 8 years old gets repaired, and any leak from the tank body means replacement whatever the age, because tanks last 8 to 12 years and a rusted-through liner cannot be sealed. The full list of causes is in why a water heater leaks, and cleanup is covered in what to do when a water heater floods the basement.
When a leaking tank needs a call right away
- You cannot stop the water at the tank valve or at the main.
- Water is near the electrical panel, outlets or the furnace.
- You smell gas, or the pilot area has been flooded.
- The leak is from the tank body and you have no way to drain it.
ZK Mechanical is a Burlington shop with TSSA-licensed gas technicians and a 24/7 emergency line with no overtime, weekend or holiday surcharge. A diagnostic visit is $90–$150 and is folded into the work if you go ahead, with a written price before anything is replaced. See water heater repair and replacement, browse more water heater answers, or call (647) 801-1252 or send a message.