Tank Type Electric Water Heater Element Check

Each water heater is required by law to have a tag, plate, or sticker showing size tank (gallons), Voltage for operation, and element size in Watts.

The manufacturer’s plate on a typical water heater could show tank size of 40 gallons of water, 240 volts, and top and bottom elements at 3500 watts each.  Each element needed 240 volts.  These sizes are typical of a heater.  The size in gallons can be 1 gallon up in size.  Common voltages in residential units are either 120 or 240 volts. 

A volt, ohm meter is needed to properly check a water heater.  These need not be expensive.  A $15- $20 unit from Radio Shack or a hardware store will suffice.  Voltage and Resistance tests are sufficient. 

With the information from the manufacturer’s plate, we are able to compute the two units needed to check the condition of the unit.  These units are Resistance in Ohms, and Current in Amps. 

Review two basic electrical formulae. 

Watts equals Volts times Amp. We know watts and voltage from the manufacturer’s plate.   W=EI or I=Wattage / Voltage

3500 = 240 X Amps. There fore dividing the 3500/240 we find 14.6 amps.

E (voltage) equals I (current in amps) X R (resistance in ohms).  E=IR or R=E/I

Using this formula, resistance equals voltage/current or 240/14.6 equals 16 ohms.

With these two new parameters: we know that the current (amps) for each element is 14.6 amps.

Also we know that the resistance in each element is 16 ohms.  The resistance in each element is checked with a VOM (volt, ohm meter). 

 MAKE SURE THE BREAKER IS THROWN AND THERE IS NO POWER TO THE HEATER DURING THE RESISTANCE TESTS.

The heating elements and thermostats are inside the outer metal covering of the heater and protected by a metal plate with two screws securing it to the outer shell.  Inside this plate is a section of insulation that must be removed.  Inside the insulation is the plastic protector for the thermostat, and heater element.  The protector snaps onto the thermostat to keep the unwary from any hot terminals and conductors.

REMEMBER, NO POWER TO WATER HEATER

To check the resistance of the elements it will be necessary to remove the plastic protector on each of the thermostats and elements. With all this removed the thermostat and element is visible. 

Remove one of the conductors from the heater element, and with an ohm meter determine the resistance between the two screws on the heating element.  A high ohm reading indicates that the element is open (not conducting electricity through the element) and not producing any heat to your water. For a 3500 watt element, the resistance should be close to 16 ohms.

From each of the element screws check resistance to the bare tank of the heater.  IF EITHER SHOWS A LOW RESISTANCE BETWEEN THE SCREW AND THE TANK, THE ELEMENT HAS BENT, BROKE OPEN, AND SHORTED TO THE TANK.  This trips either the breaker at the load center feeding the heater or the breaker on the top thermostat. Most two element heaters have this top breaker.

The same resistance tests on the top element will determine the element condition.

Proper voltage and good elements indicated by the 16 ohm resistance are necessities for hot water. 

 Check the voltage with your meter at the top thermostat. Two wires drop from the heater terminals on top of the heater and terminate on the upper thermostat.  Checking voltage at this point between the two terminals should read 240 volts as indicated on the manufacturers tag.

Barring thermostat problems, the heater should function as designed.

Most bad elements are caused by mineral buildup on the elements.  This restricts the heat from being transferred to the water and the elements to overheat.  Water around the elements to dissipate the head is necessary.  These buildups will create a waste of 60% or more in the electricity necessary to heat water.  Heating water is one of the largest portions of an electric bill.

Properly installed GMX magnetic water conditioning can remove this build up and allow no more.  Check: http://www.ellisongmx.com or http://www.baldeagletraders.com for the solution to hard water problems.

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Eddie Ellison