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Gas Water Heaters

Aug. 8, 2016

Hot water is obviously very important in our daily lives, and the water heater is one appliance that many of my clients ask me about when I perform home inspections. As a homeowner there are a few things you should know about your water heater...

Water heaters can last for decades and work fine - manufacturer warranties commonly extend up to 8 years, which is quite good considering that insurance companies may ask for replacement to reduce risk once it is 8-12 years old.

Water heaters most commonly fail by leaking from the tank itself due to corrosion. When this happens, immediate replacement is required to prevent water damage to the home. Unlike boilers, water heaters are designed to withstand corrosion caused by constant exposure to fresh, oxygenated water. This is most commonly done by lining the interior of the tank with glass, and using a sacrificial anode (magnesium or aluminum rod) in the tank to prevent corrosion of any exposed steel. This helps prevent corrosion of the tank because when two metals are connected in water, the more reactive one will corrode rather than the "nobler" metal.

So how does a water heater work? Great question.

You will see two water lines connected to the top of the water heater tank - one is the cold (inlet) line, one is the hot (outlet) line. The cold water inlet is extended inside the tank by a plastic "dip tube" that allows the cold water to be introduced at the bottom of the tank where it is heated by the burner and rises to the top due to its buoyancy.

When hot water is used, the heated water at the top of the tank moves out through the top to its destination faucet and is replaced by cold water at the bottom of the tank. When the thermostat of the water heater senses the temperature drop below its setting (usually 120-140F), it will fire the gas burner to heat the water.

A common issue with older water heaters is that they seem to "run out" of hot water quite quickly. One common reason for this is the dip tube in the tank has simply deteriorated and is introducing cold water near the top of the tank, where it exits through the outlet before it is heated sufficiently. This would simply require replacement of the plastic dip tube in the tank, which is not expensive - you should have your plumber check this before deciding to replace the whole tank.

Near the bottom of the tank you will find a drain that you can attach a hose to. It is a good idea to use this to flush the tank once per year, as sludge buildup at the bottom will impede good operation over time because it acts like a layer of insulation, making it more difficult for the burner to heat the water.

Another important component of the water heater is the Temperature/Pressure Relief (TPR) valve. This is usually on the side of the tank near the top, and should have a tube attached to it extending down to about 6 inches off the floor to prevent scalding if it does release hot water. The purpose of this valve is to prevent a steam explosion by releasing water if there is ever a malfunction that causes excessive pressure or temperature in the tank. If you find this valve leaking, it is either because there is something malfunctioning in the tank, or the valve itself is simply wearing down and needs replacement. This is also an inexpensive fix.