Water heaters, the gas side. Episode twelve of the Gas Service Animated series. One appliance that uses everything we learned this season.

Meet the season capstone: a typical draft hood storage water heater rated around forty thousand Btu per hour. Every system we studied converges here. The gas line arrives through a shutoff valve and a sediment trap, straight out of episode nine. Inside the gas control on the tank, an appliance regulator from episode one sets the manifold pressure. Combustion air from episode four feeds the burner below, while the draft hood and vent connector from episodes three and eight carry the flue gases away.

The brain on the side of the tank is the gas control: a thermostat and a gas valve sharing one body. A small pilot flame heats a thermocouple or a thermopile, generating a tiny electric signal that holds a safety magnet in. Lose the pilot and the signal dies, the magnet lets go, and the valve snaps shut — the code calls this a safety shutoff device, and one that fails to drop out must be serviced or replaced. Power vent and electronic ignition models prove the flame electronically instead, but the rule is identical: no proven flame, no gas.

No hot water and a pilot that will not stay lit is the classic call, and it deserves a systematic path. Confirm the supply first: valves open and inlet pressure present. Then read the pilot flame itself — it should wrap the sensor tip in steady blue, and a weak lazy flame points to a dirty pilot orifice or a supply problem. If the flame looks right but still will not hold, suspect a weak thermocouple, a failing safety device, or a draft sweeping through the chamber. Follow the manufacturer's procedure at every step, and if the appliance cannot be made safe, it gets shut off and tagged.

Modern storage heaters are built flammable vapor ignition resistant. The combustion chamber is sealed, and air enters only through an intake screen and a flame arrestor plate beneath the burner — so if vapors from something like gasoline or paint thinner ignite, the flame stays contained inside the chamber. That protection only works while it is intact: inspection covers, glass, and gaskets must all be in place, and the intake screen must stay clear of lint and debris. And an appliance without this listing must keep its burner at least eighteen inches above a garage floor.

With the burner running, read the flame. Healthy is steady blue with sharp inner cones. Lazy yellow tips mean starved combustion air or a burner fouled with scale and debris — the same story episode four told. After any service, prove the draft: run the main burner about five minutes, then check the draft hood relief opening for spillage with smoke or a mirror while exhaust fans and the other appliances are running, exactly as episodes three and seven taught. Spillage that will not clear means flue gases are entering the room, and that is a stop work condition.

Location matters. Clearances come from the appliance listing and the manufacturer's installation instructions, and the code states the intent behind them: nothing may interfere with combustion air, draft hood clearance and relief, or access for servicing. Where vehicles can reach the appliance, it must be located or protected so it cannot be struck. And closets and small rooms need combustion air openings sized for every appliance inside — a water heater sharing a closet with a furnace counts both inputs.

Every water heater must carry overpressure protection: a listed relief valve. The rules around it are absolute. No shutoff valve may ever sit between the relief valve and the tank, its discharge must terminate safely, and its rated capacity must at least match the heater's input. Gas techs inspect and refer — a missing, plugged, or capped relief valve is a hazard you document and hand to the plumbing side, and you never cap one yourself. A separate energy cutoff device also guards against runaway water temperature.

Before you leave, the whole season shows up on one checklist. Inlet pressure verified with a manometer at the gas control. Manifold pressure set to the nameplate value — the skill from episode seven. Input clocked at the meter the way episode two taught, never firing above the nameplate rating. Draft proven at the hood, the intake screen clean, the controls cycling with the thermostat, and every joint you touched proved leak free.

One storage water heater, and the whole season inside it: supply and shutoff, regulation, combustion air, venting, and safety controls all working together. Prove the flame, protect the vapor barrier, respect the relief valve, and verify everything before you walk away. That closes season one of Gas Service Animated. Season two is coming soon.