Tank Water Heater Problems and Repair Guides

How a tank water heater works

A storage water heater keeps a tank of water hot and ready. When you open a hot tap, heated water flows out of the top of the tank. Cold water enters at the bottom to replace it.⁠[1] The cold inlet feeds a dip tube inside the tank, which is how the new water reaches the bottom.⁠[2] Gas models heat the water with a burner. Electric models use upper and lower heating elements inside the tank.⁠[1]

Three parts guard the tank. The thermostat holds the temperature you set, and NFPA advises 120°F to lower the risk of scald burns.⁠[3] The temperature and pressure (T&P) relief valve exists to stop the tank from reaching excessive temperature or pressure.⁠[2] The anode rod slowly wears away so the glass-lined tank does not corrode. Once the rod is used up, the tank starts to corrode and in time it leaks.⁠[2]

Water also carries minerals. As it heats, dissolved calcium and magnesium fall out as lime scale and settle with soil and sand at the bottom of the tank.⁠[2] That layer lowers heating efficiency, can cause rumbling and pounding noises, and shortens the life of the heater.⁠[2]

Each of these parts can cause a symptom you can see, hear or smell. Water on the floor, a noisy tank, a rotten-egg smell and a pilot that keeps going out each start at one of these parts. The diagram on this page shows where each part sits, and the table below starts from the symptom.

Safety basics for tank water heaters

Never cap or plug the T&P valve or its discharge pipe, and never put a valve between the relief valve and the tank. The valve must stay in its own opening, and its pipe must end at a suitable drain or outside the building.⁠[2] If the valve keeps releasing water after a manual test, close the cold water inlet and have the valve replaced with a properly rated one.⁠[2]

A pilot that goes out again and again, or is hard to light, can signal a safety problem. NFPA says not to fix it yourself and to have a fuel gas professional relight it.⁠[3]

Common tank water heater problems and the first check

Start with the row that matches what you see. Each first check is safe for an owner and needs no tools.

A heater that sat in flood water is a separate case. A. O. Smith says flood damage may not be visible, and that a flooded water heater must be replaced, not repaired.⁠[2]

Tank water heater maintenance and expected life

Flush the tank to remove sediment. The A. O. Smith gas manual recommends draining and flushing every 6 months.⁠[2] Its flushing steps follow this order:

1. Turn off the electrical supply to the heater.
2. Leave the cold water inlet open, run a nearby hot tap until the water is no longer hot, then close the tap.
3. Connect a hose to the drain valve, secure the far end at a drain and open the valve.
4. Let water flow under supply pressure until it runs clean, then close the valve, refill the tank and restore power.

Other models may add steps, so follow the manual for your heater.

Check the anode rod. The same manual says to remove the rod for inspection every 3 years, or every year if your water is softened.⁠[2] It calls a rod depleted when most of its diameter is under 3/8 inch. Bare core wire along about a third of its length is the other sign.⁠[2] Never remove the anode for good. A. O. Smith says that voids the tank warranty, and it offers a special rod for water that smells like rotten eggs.⁠[2]

Test the T&P valve. A. O. Smith recommends checking that it works every 6 months, with no one near the discharge outlet, because the water may be extremely hot.⁠[2]

Watch for thermal expansion. Heated water expands, and in a closed system with a check valve or pressure reducing valve the pressure rises with it.⁠[2] That can make the relief valve drip and can cause early tank failure, so A. O. Smith requires a properly sized expansion tank on closed systems.⁠[2]

Set the temperature with care. University of Maryland Extension says 120°F is enough for most households and can cut water heating energy use by 6 to 10 percent.⁠[1]

Expect a tank to wear out. A 2007 NAHB study put the life of a gas water heater at about 10 years and an electric one at about 11.⁠[4] Tankless units age on a different curve; all water heater repair guides cover both types.