Written by:
Wes Kelley, Certified Inspector
7 Oaks Home Inspection, LLC

The lowly water heater is rarely thought of by many homeowners until they happen to step in to an icy shower some fateful morning. A few water heaters make a more dramatic rembrance, by exploding! By learning a few things about the mechanics of a water heater you should be able to ensure a long lasting hot water supply and avoid a potential bomb.

According to most manufacturers, relief valves should be periodically tested every six to twelve months by lifting the manual release lever on the TPR valve. I should caution you that in an older tank, testing the TPR valve might actually cause the seat to crack or some built up calcium might become lodged causing the seat not to close and start dripping. A TPR valve in good working order is very necessary to ensure home safety. Water heaters can become bombs if the water pressure gets too high and a TPR valve does not function as designed. A sticky or defective valve can allow tank pressure to build to the point of explosion. If you turn on your hot water and air comes out and or you hear gurgling you might have the first warning signs that your tank is “boiling hot” and unsafe.

There are two questions a home inspector frequently gets regarding the water heater. The first question is, “Why do I have a ‘rotten egg smell’ coming from the hot water tap?” To understand the problem you must understand the mechanics. In the top of the tank is the anode rod. This rod is a metal rod consisting of magnesium and sometimes aluminum. These metals help protect the water tank from corroding because electrolysis eats away at this rod rather than the metal tank itself. However, bacteria can react with the decaying magnesium anode rod causing the formation of hydrogen sulfide hence, the rotten egg smell. The cure for “rotten egg smell” is achieved by replace the magnesium anode rod with an aluminum rod.

The second question often asked is, “Why is water dripping from the discharge tube of my water heater?” This tube is located on the outside of the water heater down line from the temperature pressure relief valve. This is also known as the TPR valve, pop off valve or relief valve. The TPR valve is usually mounted on top of the tank but sometimes it is mounted on the side. These valves can begin to drip water for two reasons. One the pressure in the tank is exceeding the set point on the TPR valve or the valve itself has become defected. As water is being heated in a closed container, (water heater), the heated water molecules expand causing pressure to build in the tank. When pressure builds above the pre-set pressure of the TPR valve, (about 120 psi), the valve will open and allow pressure to escape. So one reason for water discharge is that the TPR valve is equalizing internal pressure. However, no homeowner wants to deal with wet floors and possible mold issues. The solution for this particular problem is to install an expansion tank in the cold water line between the back flow valve and the water heater. These small tanks give the extra “expanded” water a place to go which stops the water dripping from the discharge tube.

The second reason for water leaking from the discharge tube is not related to pressure but a defective valve. As the valve gets older the seat sometimes cracks or a particle from the tank gets stuck in the seat holding it partially open. Either one of these problems will cause dripping from the discharge tube. A qualified plumber will be able to correctly diagnose and repair your dripping discharge tube.

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