Every gas tank water heater shares the same basic anatomy, and knowing what each part does helps a homeowner understand what a technician is actually checking during service.
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Quick answer
A gas storage water heater's core anatomy includes an insulated steel tank, a burner and gas control valve underneath it, an igniter or pilot with a flame sensor, a dip tube feeding cold water to the bottom, an anode rod for corrosion protection, a temperature and pressure relief valve, and a draft hood or vent connector carrying exhaust outside. Each part has a specific job, and most common symptoms, from rumbling noises to inconsistent temperature, trace back to one of these components wearing out or needing attention.
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The tank itself is welded steel with a glass, or vitreous enamel, lining bonded to the interior surface, intended to keep the steel from contacting water directly. Around the outside, a layer of foam insulation, wrapped in a steel or plastic jacket, slows heat loss so the burner does not have to fire as constantly to hold temperature. This lining and insulation are what allow the tank to hold hot water efficiently for hours between burner cycles.
Beneath the tank sits the burner, fed by a gas control valve that opens and closes based on signals from the thermostat built into that valve. Ignition is provided either by a standing pilot light that stays lit continuously, or by an electronic igniter that lights the burner only when heat is called for, depending on the model. A thermocouple or flame sensor confirms a flame is actually present once ignition occurs, and if it does not detect one, the gas valve is designed to shut off rather than continue releasing gas.
This flame-proving safety function is one of the most important parts of the whole appliance, since it is specifically there to prevent unburned gas from accumulating if ignition fails for any reason.
| Component | Location | Function |
|---|---|---|
| Dip tube | Extends from the cold inlet to near the tank bottom | Delivers incoming cold water to the bottom rather than mixing at the top |
| Anode rod | Suspended through a fitting at the top | Corrodes sacrificially to protect the tank's steel lining |
| Drain valve | Near the bottom of the tank | Allows the tank to be drained for flushing sediment or servicing |
| Hot outlet | Near the top of the tank | Draws the hottest layered water to supply fixtures |
The temperature and pressure relief valve, usually on the top or upper side of the tank with a discharge pipe running toward the floor, is a critical safety device that opens automatically if either the water temperature or the internal pressure rises above a safe threshold. It should never be capped, plugged, or have its discharge pipe blocked. A relief valve that drips occasionally can be doing exactly what it is designed to do under certain conditions, but persistent dripping should be assessed by a technician rather than ignored or worked around.
Combustion exhaust leaves the tank through a draft hood at the top and travels up a vent connector into a flue or chimney. This is a natural-draft system on most standard tanks, relying on the buoyancy of hot exhaust gas rather than a powered fan, which is why proper flue sizing, a clear path free of obstruction, and adequate combustion air in the mechanical room all matter for safe, correct operation. A blocked or corroded vent connector, or a mechanical room starved of combustion air because of a renovation that sealed up the space, can affect how safely the appliance vents.
In many older Vancouver-special homes, this venting shares a chimney originally built for multiple appliances, and changes elsewhere in the home's heating system can affect how that shared flue performs for the water heater still connected to it.
A homeowner can safely glance at the flame through the sight glass or viewing window, if the model has one, and note whether it looks steady blue rather than yellow, orange, or flickering. Noticing rust-coloured water, a puddle at the base, or a burning smell are also useful, safe observations. Removing the burner assembly, testing the thermocouple, replacing the anode rod, or working on the gas valve itself all involve gas connections and are licensed gas fitter tasks.
Safety note
A gas storage water heater burns natural gas and is vented to the outside, so any work on the gas control valve, burner, thermocouple or igniter, or venting must be done by a Technical Safety BC licensed gas fitter. If you ever smell gas, notice soot near the draft hood, or suspect a venting problem, leave the home immediately and call FortisBC at 1-800-663-9911 before doing anything else.
It is a sacrificial rod of reactive metal that corrodes in place of the tank's steel lining, extending the tank's usable life.
The relief valve is a critical safety device that releases pressure or excess temperature; blocking it removes that protection entirely.
A standing pilot stays lit continuously as a small flame, while an electronic igniter lights the burner only when heat is called for; both rely on a flame sensor to confirm ignition before the gas valve stays open.
It routes incoming cold water to the bottom of the tank so the coldest water is heated first, rather than mixing immediately with the hot water layered near the top.
It requires draining the tank and removing a fitting that is often torqued tightly, so it is generally best left to a licensed technician.
A clean flame should burn blue; a yellow or lazy flame can indicate a combustion air or venting issue and is worth having checked by a technician.
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