Quick Answer
On a gas water heater, the most common causes are a blown-out pilot light, a failed thermocouple, or a faulty gas control valve. On electric units, it's usually a tripped breaker, a failed heating element, or a bad thermostat. If you get some hot water but it runs out fast, suspect sediment buildup or a broken dip tube rather than total failure.
No hot water is one of the few HVAC problems that announces itself in the shower. The good news: the cause is usually one of a half-dozen well-known failures, and several are safe to check yourself before calling anyone. Start by identifying whether your unit is gas or electric — the diagnostic paths are different.
Gas water heater: check these first
- Pilot light out — look through the sight glass at the bottom. Relight per the label instructions. If it won't stay lit, the thermocouple has likely failed ($150–$300 to replace).
- Gas supply — confirm the gas valve on the supply line is open and other gas appliances work. If nothing gas works, contact Enbridge.
- Gas control valve failure — if the pilot lights but the burner never fires, the control valve may be done ($400–$600). On a 10+ year tank, that price usually means replace the unit.
- Power-vent units: check the wall outlet and breaker — the vent fan needs power, and the unit locks out without it.
Electric water heater: check these first
- Breaker — a water heater on a tripped 240 V breaker is the most common 'failure.' Reset once; if it trips again, stop and call — that's a short.
- High-temperature reset button — behind the upper access panel; press it. Repeated tripping means a failing thermostat or element.
- Heating elements — the upper or lower element burns out over time; only lukewarm water often means the lower element is gone ($200–$400 replaced).
Warm-but-not-hot, or runs out fast?
Partial hot water points to different culprits: heavy sediment buildup insulating the burner from the water, a broken dip tube letting cold inlet water mix straight into the hot outlet, or a thermostat set too low (60°C at the tank is the safe standard). Our water heater maintenance guide explains the sediment problem and how flushing prevents it.
When to stop DIY and call
- Any smell of gas — leave the house and call Enbridge's emergency line first
- Water pooling around the tank — corrosion has likely breached the tank; replacement is the only fix
- Breakers or reset buttons that trip repeatedly
- Anything involving the gas control valve or burner assembly — in Ontario this is licensed-technician work
ZK Mechanical offers same-day water heater repair across the GTA and 24/7 emergency service when there's no hot water and no time. If the unit is past 10 years old, we'll give you an honest repair-vs-replace comparison before any work — contact us or call (647) 801-1252.
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