How a Gas Tank-Type Water Heater Works

By Thornton Plumbing and Heating

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Tank-type water heaters are common amongst homes and with regular maintenance can last a lifetime! Although tankless water heaters are rapidly becoming more popular, tank-type water heaters are still the homeowners’ first choice in Salt Lake City, Utah.

You can purchase a tank-type water heater in either electric or gas. But gas is the ideal choice as it requires a lower initial cost and lower operating costs.

Basics of Gas Water Heater Operation

A tank-type water heater boils cold water and stores the hot water until the faucets and fixtures need it. Gas water heaters work by the law of convection. The cold water enters the tank through the cold water supply tube, which forces a constant flow of cold water into the tank.

Below the sealed tank is a gas burner that heats the cold, dense water at the bottom of the tank. As the water heats, it rises in the tank, and the hot water discharge pipe draws the water to supply it to faucets and fixtures that need the hot water.

A gas regulator assembly controls the gas burner. The gas regulator assembly is mounted on the side of the heater. And it hosts a thermostat that measures the temperature of the water inside the tank.

The thermostat automatically turns the heater on or off as required. An exhaust flue runs through the tank’s center to allow exhaust gases up through the tank and out of the houses via a chimney or vent.

In the hollow flue is a spiral metal baffle to capture heat and transfer it to the water, making this appliance much more efficient.

The Tank

A water heater’s tank includes a steel outer jacket to enclose a pressure-tested water storage tank. This internal tank comprises high-quality, durable steel with glass or plastic bonded to the inside surface to prevent rusting.

Between the inner storage tank and outer tank jacket is a layer of insulation to reduce heat loss. Alternative to the insulation, you can add a fiberglass insulation tank jacket to the outside of the water heater.

Inside the Tank

Aside from the long cold-water tube and the shorter hot water discharge pipe is a range of functions inside the tank.

For glass-lined tanks, there is a metal rod inside the tank. This rode is usually made of magnesium or aluminum. We call this metal rod is called a sacrificial anode. The anode rod is bolted and tied to the top of the tank and extends deep into the tank.

The role of this rod is to draw rust-causing ions from the water and into it. This function prevents the tank from corroding. However, some tanks don’t have an anode rode and instead have a hot water outlet pipe coated with magnesium or aluminum.

If the hot water leaving the tank is discolored or smells, the anode rod might be consumed.

Cold Water Supply Pipe and Hot Water Discharge Pipe

Fixed on top of the tank are two pipes- a hot water discharge pipe and a cold water supply pipe.

  • The Cold Water Supply Pipe. The tank receives cold water via a cold water supply line controlled by a shutoff valve. Find out where the shutoff valve is so you can close it when required. Shutting off the cold water supply will shut off the water completely, as the tank needs cold water for the heater to supply boiling water. Usually, the cold water shutoff valve has a blue handle.
  • Hot Water Discharge Pipe. This is the pipe that supplies your faucets and appliances with hot water. The shutoff valve for the hot water discharge pipe is typically blue.

Gas Regulator and Burner Assembly

A pipe delivers the natural gas or propane heating your water and has its own shutoff valve. The shutoff valve is made from steel black pipe or copper tubing. You need to know where this shutoff valve is so you can turn off the gas when needed.

This gas line powers a gas regulator which hosts the water heater’s thermostat. Also, this valve supplies gas through an additional tube to the pilot light. The pilot light ignites the burner when the regulator valve and thermostat require it to.

To the gas burner assembly, gas flows from the gas regulator. You can access this gas through the metal panel at the bottom of the heater’s case. This assembly comprises the pilot light and gas heater.

The gas flames should be half an inch high with blue tips. Furthermore, in the pilot light is a thermocouple or flame sensor-a small valve that converts heat to an electric impulse.

A thermocouple or flame sensor is an essential safety feature as it recognizes the pilot flame and prevents the burner from receiving gas when there is no pilot flame to ignite it. Replacing a thermocouple or flame is seamless!

Exhaust Flue

The exhaust flue is the hollow cylinder in the center of the tank we discussed earlier. This flue serves two primary purposes. It exhausts combustion gases from the burner and helps heat the water in the tank. The flue must be exhausted to outdoor requirements, and there are code requirements for constructing a flue.

Temperature and Pressure-Relief Valve

The temperature and pressure-relief valve is another crucial safety feature. It works the same way as a radiator cap on your car. This valve relives excess temperature or pressure build-up in the tank if it gets closer to the tank’s limit.

You can find this valve on top of the tank, and to test the valve you need to lift it slightly for the tank water to leave via the overflow pipe. If this does not happen, you need to replace the valve.

Tank Drain Valve

Unfortunately, over time your hot water tank might build up sediments at the bottom of the tank, which can cause various issues.

A water heater riddled with sediments will not operate efficiently, and you might hear bubbling or gurgling sounds often because of the moisture-saturated sediments boiling.

To remove these sediments and prevent dire issues, drain your tank regularly with a tank drain valve.

  1. Turn the gas pilot control to the “pilot” setting.
  2. Shut off the water heater’s cold water supply.
  3. Open the nearest hot water faucet.
  4. Attach a garden hose to the drain valve and place the hose in a floor drain or sink.
  5. Open the tank drain valve to allow the water to drain from the heater’s tank. It is common to see discoloration as you drain the sediments. In severe cases, you might need to drain the tank twice.
  6. When the tank is empty, shut off the tank drain valve. Open the cold water supply to refill the tank and turn the gas control valve to the “ON” position and ensure the gas ignites.

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