Trouble Shooting Water Heaters - How Does a Water Heater Work?

This is a trouble shooting guide for water heaters. Do not attempt to repair a water heater if you don't know what you are doing!

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Helpful water heater trouble shooting guide and information

Take all safety precautions when working on water heaters.  Water heaters can be very dangerous.

For more detailed repair and trouble shooting help see our pages on electric and gas water heaters.

Water heater sediment buildup

In a water heater the heating of the water causes calcium carbonate to precipitate out and settle to the bottom of the tank. Steam bubbles can form under the layer of sediment when the burners come on causing popping and other noises. It can also reduce the amount of water your tank holds. Regular flushing will help prevent sediment build up.  This layer of minerals will not harm anything, and contrary to general thinking, has been shown by studies, not to decrease the efficiency of the water heater. 

Not producing enough hot water

Check for a broken dip tube, wrong setting on a thermostat, a defective thermostat, burned out heating elements (electric), or a heavy build up of sediment which reduces the capacity of the heater.  A broken dip tube can allow the incoming cold water to mix with the outgoing water at the top of the tank, causing the water to be cooler than expected.  Electric water heaters generally have two heating elements, one at the top of the tank and one at the mid-level or bottom. If one burns out you will suffer lower hot water temperatures and/or running out quickly.

Dip tube

The dip tube is a long slender tube that fits down into the water heaters  inlet, and usually has a small hole about 6 inches from the top. The dip tube directs the incoming cold liquid down to the bottom of the tank.  If the dip tube is broken, the incoming cold liquid can mix with the out going hot water and cause it to seem as though you are running out. Replacing the dip tube is in theory very easy, but in practice rusted old pipes can create problems.

Noisy tank

Noise coming from gas water heaters can often be caused by the sediment build up in the bottom of the tank. Steam bubbles form under the sediment. The thumping and popping noises are created by the bubbles escaping from under the sediment.  Sizzling noises can be caused by condensation dripping onto the hot burner. Generally these problems are not of a serious nature except that you hear them.

Thermal expansion

Heating water causes it to expand. If the inlet to the water heater is not blocked by a check valve, pressure reducing valve, or other device, the increase in volume simply goes back into the water main or storage tank if you are on a well system. If the inlet is blocked, this increase in volume will cause an increase in pressure, sometimes to dangerous levels.  If the T- P valve doesn't function correctly the water heater could explode with deadly consequences.

The T&P (Temperature-pressure) valve relieves this pressure by discharging some water.  A thermal expansion tank can be installed in the line that will absorb the increase in volume, preventing the relief valve from discharging unnecessarily.

T&P valves are strictly an emergency measure and should be replaced every 2 years.  At 180 degrees, the temperature that the T&P valve opens, damage can occur to your system and you may have voided the warranty on your water heater.

The improper installation of backflow preventers can block the thermal expansion leading to operation of the T&P Valve.

Water Hammer

When water is traveling in the pipes it has kinetic energy (energy of motion).  When a valve shuts off suddenly and stops the moving water, a shock wave results.  This shock wave produces a hammering noise in your pipes and is known as "water hammer".

Water hammer most often occurs when a valve shuts off suddenly.  Commercial arrestors are available to combat this problem. The arrestors consist of a small pressurized air chamber within a cylinder plumbed into the plumbing near the valve causing the problem.  Most hardware stores and plumbing wholesale houses carry them. 

Sometimes if the piping is sagging and the water hammer is not too severe, then supporting the pipe solves the problem.

Milky color

Water contains dissolved oxygen and other gases.  When it's heated it has less ability to hold these gases and when the pressure is lowered  as the water comes out of the tap these gasses can form tiny bubbles giving the liquid a milky appearance.  Letting it stand for a few minutes will allow these bubbles to rise out of the liquid and it resumes its clear appearance.

If you live in an earthquake prone area then be sure to strap the tank to the wall to prevent damage and possible injury during an earthquake.

Stinky hot water

If your hot water has the odor of rotten eggs, then you have bacteria in your water heater that is reacting with the magnesium anode in your water heater,  producing hydrogen sulfide gas which smells like rotten eggs.  Change the anode to an aluminum one, the bacteria can't react with the aluminum.