Electric Water Heater Problems - Storage Tank Type

Electric water heaters and the electrical problems they can have are today’s topic. The electrical system for an electric water heater is fairly simple, and easy to trouble shoot.

A typical water heater will have two heating elements and two thermostats plus a high limit switch.

Let’s start with the high limit switch. The high-limit switch is a thermal circuit breaker. When it gets too hot, it will trip, and a red button will pop out. So if suddenly you have no hot water, the first thing you might want to check is that red button. Push it in and see if that gets the heater going again.

There are two thermostats on a typical unit, one near the top and one near the bottom. The thermostat near the top of the tank is like a temperature controlled single pole double throw switch. That means it is either feeding electricity to the top heating element, or if it is off, it is directing the electricity down to the lower thermostat.

Understanding the operation of the heater will help in troubleshooting. Let’s assume that you just filled the bathtub with hot water, and so your water heater is basically full of cold water. Both the upper and lower thermostats will be turned “on” because the temperature will be below the set points of the thermostats.

Electricity will flow from the mains through the upper thermostat and into the upper heating element, through the element, and back into the mains.

Once the water in the top of the water heater has reached the set point on the upper thermostat, the upper thermostat will shut off the electricity to the upper thermostat, and send it down to the lower thermostat.

The lower thermostat is “on” since it has not warmed up above the set point. Because it is “on” it sends the electricity to the lower heating element and the electricity flows through the element and back to the mains.

When the water in the lower part of the electric water heater reaches the set point temperature of the lower thermostat it shuts off the electricity to the lower element and nothing else happens until the water in the heater lowers below one or the other set points.

Electric Water Heater Troubleshooting

If you have no hot water:

As I mentioned earlier, the first thing to try, in my opinion, is the high limit switch. Push the button and see if the heater begins heating the water.

If that does the trick, the next thing you need to worry about is why the high limit switch tripped in the first place. Did the water temperature get too high? If so why?

A defective upper thermostat that sticks in the “on” position is one thing that will cause the high limit switch to trip. Also a defective high limit switch could be the source of the problem.

Certain usage patterns (frequent small draws) can cause what is known as “stacking” where the water at the very top of the heater gets hotter than it should.

If the high limit switch button is not popped out or if pushing it has no affect, then it’s time to move on to checking the heating elements.

Testing Electric Water Heater Heating Elements

The first thing to do is of course; turn off the electricity to the water heater.

Next you need a simple ohm-meter. Like a cheap Radio Shack multi-meter.

Disconnect one of the two wires to the heating element and then read the resistance between the two heating element terminals.

The heating elements should have an electrical resistance of less than 50 ohms. You don’t have to worry about the amount of resistance though, it will either have some resistance, or it will have an infinite amount. If the needle moves, the element is ok. If it doesn’t, the element is burned out.

If the heating elements are ok, then it’s most likely a bad thermostat. Check and make sure none of the wires are broken or loose under a terminal.

Testing the Thermostats

The electricity comes into the water heater and goes directly to the high limit switch… usually the top two terminals on either side of the high limit switch. Normally the high limit switch is stacked above the upper thermostat.

The upper thermostat has one wire that connects directly to the upper heating element, and one wire that connects to the high limit switch. It has another wire that goes down to the lower heating element.

With a below set point temperature in the water heater, the high limit switch should be sending electricity to the upper thermostat, which should in turn be sending it to the upper heating element.

With the electricity still turned off to the water heater, check the resistance between the top wire that goes from the high limit switch to the mains, and the high limit switch terminal that leads to the upper thermostat. The resistance should measure zero. If not, the high limit switch is bad. (or the red button needs to be pushed in)

If it does read zero, then check the resistance between the terminal on the upper thermostat that connects to the high limit switch, and the terminal that lead so the upper heating element. It should read zero. If not, the upper thermostat is bad.

To check the bottom thermostat check the resistance from the lower thermostat terminal that connects to the upper thermostat, and the terminal that goes to the lower heating element. It should read zero. If not the lower thermostat is bad.

That’s it. You should have found the problem by now if it is electrical in nature.