Quick answer
A water heater that smells like gas has a leak until proven otherwise: leave the house and call Enbridge Gas at 1-866-763-5427 or 911 from outside, and do not relight, switch or unplug anything on the way out. The usual sources are the flex connector or union, the gas control valve and the pilot tube fitting. Only a TSSA-licensed gas technician may repair and leak-test it.
If your water heater smells like gas, treat the smell as a leak first and a puzzle second. Natural gas has no odour of its own; the skunky, rotten-egg smell is mercaptan, added so that you notice a leak long before there is enough gas in the air to ignite. A water heater in good order gives off no gas odour, burner on or off.
What to do right now if you smell gas at the water heater
- Get everyone out of the house, pets included, and leave the door open behind you.
- Do not relight the pilot, flip a light switch, unplug a power-vent blower, press a garage door opener or start a car in an attached garage. Each one can make a spark.
- From outside or a neighbour's house, call Enbridge Gas emergency at 1-866-763-5427, or 911.
- Stay out until the responder says the house is safe. Enbridge shuts off and tags the appliance or the meter; it does not repair the water heater.
On rural lots that heat with propane, as in parts of Kilbride, Campbellville, Carlisle and rural Caledon, call the emergency number on the tank or your propane supplier, or 911. Propane is heavier than air and settles at floor level in a basement, which is exactly where a water heater burner sits. The full evacuation steps are in what to do if you smell gas.
Where a gas water heater leaks from
- Flex connector or union: the corrugated connector or threaded union between the shut-off valve and the tank gets bumped by storage boxes, kinked during a tank swap or disturbed when the tank is moved. A leak here smells whether the burner is running or not.
- Gas control valve: the box with the temperature dial on the front of the tank can seep at its inlet thread, at the outlet to the burner tube, or through a worn internal seat that passes gas with the dial turned down.
- Pilot tube fitting: the thin tube from the control valve to the pilot is held by a small compression nut at each end. A nut loosened during a thermocouple change, or a tube cracked from being bent, leaks a small steady amount under the tank.
- An unlit pilot: on a standing-pilot tank the thermocouple should close the pilot gas when the flame dies. A faint smell around a dead pilot means that safety is slow or has failed.
- The shut-off valve stem and drip leg cap: old pipe compound dries out, and a valve stem can weep after being turned for the first time in years.
Gas in the air, or rotten eggs in the hot water?
A sulphur smell that appears only when you run a hot tap is not a gas leak. It is hydrogen sulphide, produced when bacteria in the tank react with the anode rod, and it comes out of the water instead of hanging in the basement air. It turns up most on private wells and in tanks that have sat unused, and the fix is a flush and a different anode, covered in why hot water smells like rotten eggs.
The test is location. A smell at the hot tap that is absent at the cold tap and absent beside the tank is water chemistry. A smell in the air beside the tank, along the gas line, or through the basement with no taps running is mercaptan until a gas detector says otherwise. A dry floor-drain trap can mimic it with sewer gas, but that is a call to make after the utility has checked, not before.
What a water heater gas leak repair costs
The price depends on which joint or part is leaking, and a loose fitting costs far less than a failed control.
- Diagnostic service call: $90–$150, typically credited toward the work if you proceed.
- Remaking a leaking union, flex connector or pilot tube fitting, followed by a leak test: the low end of the $150–$800 water heater repair range.
- Gas control valve replacement: $400–$600.
- Thermocouple replacement when the pilot will not hold: $150–$300.
- Tank replacement when the heater is near the end of its 8–12 year life or the control is no longer available: $1,200–$2,500 installed.
Who is allowed to fix a gas leak at a water heater in Ontario
Only a TSSA-licensed gas technician may repair gas piping or controls and put the appliance back into service. The utility's responder makes the house safe and leaves a tag; the repair is your contractor's job. Our technician traces every joint from the shut-off to the burner with an electronic combustible-gas detector, confirms the source with leak-detection solution, makes the repair and tests again before relighting.
Do not put a wrench on the union or brush soapy water on the fittings while the smell is present: if gas is escaping, the right place to be is outside. If the tank is a rental, the rental company is responsible for the repair, and the number is on the sticker on the jacket. If the appliance or the meter was tagged off, getting your gas turned back on after Enbridge shuts it off explains the paperwork.
ZK Mechanical takes gas-smell calls on the 24/7 line with no after-hours, weekend or holiday surcharge. Once the utility has made the house safe, call (647) 801-1252 for emergency service or gas water heater repair. If the heater is tagged off and you can manage until morning, book the repair online.