Watts up, Doc?

Troubleshooting electric water heaters can be something of a mystery and can be quite deadly if not serviced by knowledgeable mechanics. This column is not intended for the do-it-yourself market, but rather, for service mechanics already familiar with these products and electricity. Once you master a few basic formulas and develop safe working habits, repairing electric water heaters can be a nice addition to your service division and virtually free from callbacks if you follow this advice. We’ll work with residential 220-Volt, single-phase, dual-element models in this column.  

Begin your troubleshooting by asking leading questions regarding the homeowner’s perception of the problem. With the knowledge you already have concerning water heaters, you can often diagnose the problem prior to entering the mechanical room. Knowing the difference between dip tube symptoms, teenagers and water heater performance issues can save a world of grief regarding potential callbacks.

Checking an electric water heater’s vital signs requires the panels to be removed to access the elements, controls and wiring connections. Turn off and lock out the breaker if there is any chance of someone inadvertently energizing the circuit. This is also a good time to check for inquisitive children, adults and pets. Never leave an open wiring connection energized while running to the truck or supply house for parts or tools. Once the insulation and covers over the connections are removed, visually inspect the components for corrosion, burned-off wires and loose connections. This is the time to check for voltage to verify the breaker was labeled correctly! If the homeowner hasn’t run hot water during the past hour, feel the tank adjacent to the upper and lower element connections.

Remember this phrase: “Ride the WAVe (Watts = Amps x Volts).” With the power back on, you can easily ascertain two of the three items needed to troubleshoot the elements. If you’ve got 220 volts and a 4,500-Watt element, then your amp-meter should be showing 20.45 amps. Caution — placing your test leads on the two-element terminals and obtaining a zero voltage reading, doesn’t mean there isn’t any voltage present. Typically, the thermostat switches off only one leg of the 220-Volt current. Make it a habit to check between each terminal and a ground source with the meter test leads, often the tank itself. Don’t forget that the 115 Volts will back-feed through the element and the circuits. Your meter can also be used to check the thermostat contacts and will show a zero voltage reading across the circuit when it is in the closed position providing there is no resistance in the contacts. When the thermostat is satisfied and in its open position, you will see a full voltage reading across these two terminals. The same applies to the high-limit switch.

You can also check for ohms of resistance through an element to check its integrity, but I strongly recommend disconnecting both of the wires prior to trying this route. Electric meters that don’t have adequate internal protection go boom if you forget to turn off the voltage prior to checking ohms. This usually happens about two thousand miles from the nearest supply house and always in front of the customer, not that I’ve ever done that! Try explaining that troubleshooting method to a skeptical customer. “Honest lady, I was smoke testing my meter.”

Knowing that you’ve got 20.45 amps and 220 volts indicates the ohms should be 10.75. (Ohm’s law: Volts = Amps x Ohms)

Why do electric water heaters take so darn long to heat cold water? It’s elementary my dear Watts-on! Convert watts to Btu, as in the above 4,500-Watt element, and you get an input of just 15,358.05 Btu/h (Watts x 3.4129 = Btu/h). Most 220-volt water heaters are equipped with an upper and lower element that will not be energized at the same time due to the amperage draw, so you’re limited to the input of only one element.

OK, so you’ve gone through the tests above and diagnosed a deceased lower element. The heater is more than five years old and you’re a good 20 miles from the shop. You carry a dual set of elements plus the upper and lower thermostats on your truck. Your established policy is to warranty repairs for a period of one year. Do you then drain the tank and replace only the lower element? Not unless you’re a glutton for punishment. The majority of customers, at least this has been my personal experience, will not willingly pay for the second trip when the other element or thermostat fails within that one-year period. For the relatively minor additional expense of the second element and thermostats, you’re worlds ahead of the game by including them on the first trip. As an added bonus, removing the second element gives you a bird’s eye view of the anode rod and dip tube. You can visually check the dip tube by observing full flow while the tank is empty. The lower element port is also a great access point for the removal of sediment. While the tank is drained, check the thermal expansion tank for proper air charge.

After you’ve refilled the tank with water and restored electrical power, take a moment to test the relief valve. Water heater thermostats are typically set to operate in the 120° to 130° range. Given the time constraints we all face, it’s not always possible to wait for full recovery before testing the final water temperature. Now is the time to carefully explain to your customer that having new elements and thermostats will also mean having a different water temperature. Stress the need for safety with the elderly, children, diabetics and themselves regarding possible scalding.