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Water Heater,Gas,Detailed Operation

/Water Heater,Gas,Detailed Operation
Water Heater,Gas,Detailed Operation 2018-08-14T12:54:30+00:00

Water Heater – All the details about how a gas water heater works, with a diagram showing all the parts. Includes TPR valve, Anode, Thermostat, Thermocouple, gas valve, dip tube and more.


Water Heater Operation

A gas water heater is the most prevalent type of heater. Gas water heaters reach full temperature about twice as fast as electrics, and cost about half as much to operate due to the lower cost of gas.

The tank should be tied to a structure such as the wall in earthquake prone areas to prevent a serious gas fire if the tank falls over and ruptures the gas line.


Water Heater – How It Works With All the Details (gas)


A water heater can exhibit some strange behaviors

Not so fast.  Water heaters have some interesting behaviors and can often be quite puzzling when something goes wrong.  Let’s see how a gas water heater works.

A typical 40 or 50 gallon gas water heater consists of a tall cylindrical tank, with a hemispherical fire box on the bottom with the flue (chimney) leading from the firebox through the center of the tank and out the top.  The firebox is of course where the gas burner is located.  There is a pilot light next to the burner, and a thermocouple is placed in the flame from the pilot light.

Thermocouple keeps the pilot light lit

A thermocouple produces a small electric current that tells the gas control valve that the pilot light is burning. If the pilot light goes out, the thermocouple stops producing the electric current, and the gas valve will not turn the gas on to the burners. In order to produce enough current to hold the valve on, it has to be very hot.  That is why you have to hold in the button for so long when lighting a pilot light.

The thermostat controls the water temperature

Near the bottom of the tank there is a thermostat inserted into the side of the tank. The thermostat senses when the temperature drops below a certain pre-set level, and this causes the burner to come on.  When the desired temperature is reached, the thermostat shuts off the burner. Typically there is a control knob to set the temperature to warm med or hot.

The dip tube is critically important


Without the dip tube in place the cold water coming into the water heater can just travel a few inches to the side and exit through outlet. Some mixing occurs of course, but the water temperature is low, and it can seem as though your water isn’t getting hot, just warm, and/or you run out quickly.

Cold water coming into the water is sent through the dip tube to the bottom of the tank where the thermostat is located.  Running even just a gallon out of the hot water tap can cause a drop in temperature thermostat, turning on the gas valve. The pilot light ignites the gas and water heating begins.

Hot water stacking





Thermal expansion tank



Usually local codes call for the output of the T&P valve to be piped down to near the floor, or outside to the ground, so no one gets scalded if they happen to be standing near the water heater when the valve opens.

What is sediment and where does it come from?



If you live in an area with hard water, over time your sediment can build up to pretty significant levels. You often hear that a build-up of sediment reduces the efficiency of your heater, but it doesn’t have much impact.  If the sediment interfered with the transfer of heat from the firebox to the water, and as a result more heat leaked out of the firebox or went up the chimney, then the efficiency would be reduced.

Instead, the heat just passes through the sediment into the water and no reduction in efficiency occurs.  However, if the buildup is large, the amount of water held by the water heater is reduced, so you could run out of water more quickly.

Popping noises and other strange sounds

Loud popping and other odd noises occur when gas bubbles form under the sediment due to the water in contact with the tank bottom turn to steam. It doesn’t hurt anything, but it can be annoying.  Sizzling noises could be condensation dripping onto hot metal parts.

Those who live in hard water areas might want to flush the water heater once a year or so. If you flush it, and there isn’t much sediment, you might just want to let it accumulate.

The anode protects against corrosion


Smelly hot water — rotten egg odor



Drain valve – replace it with a ball valve
