Water Heater Operation

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    • #273651
      Avatar photoMasterPlumbers

        I just recently replaced two water elements (240V/4500W) to my RHEEM
        water heater. Once I bled the lines, I initiated power to the heater and conducted voltage checks across the heater element leads. The bottom element read 240V, but the top read very low voltage (millivolt range). After a while, the water heater thermostat clicked so I conducted another voltage check and both elements read very low voltage (millivolt range) The elements appear to be working fine because I have hot water. But, I keep thinking that the bottom element is the only one working due to the voltage being there once I applied power to the unit. Could I have a faulty thermostat on my top heating element? How do I check? What is the sequence of operation for the heating elements working together and where can I get this info??

      • #288223
        Avatar photoGuest

          John: The sequence of operation for your Rheem water heater is as follows when initiated on a cold tank of water.
          The upper thermostat will supply energy by way of the blue and yellow wires to the upper element.
          (If the power supply is 220 volts and the heating element 4500 watts,
          a current of 20 amps(approx.) should be indicated)
          Once the upper part of the tank has been heated to the upper thermostatic setting, the power will be then terminated to upper element and the energy will be directed through the red and black wires to the lower thermostat and element.
          The lower element will continue heating the water at the bottom of the tank untill the lower thermostat is satisfied.
          The lower element then will maintain the heat of the water in the tank at that setting, unless sufficient water is drawn from the tank to energize the upper thermostat again.
          Only one element is energized at a time with 220 volts..one leg of the 220 supply voltage is always present(110 volts) at the element terminals, the other leg is controlled by the thermostat when heating is called for.

        • #288224
          Avatar photofourth year

            If the bottom element started heating immediately after you turned on the power, then the contacts on the upper thermostat were fused when the element burned out. If you use up all the hot water in the tank so that the upper element should operate, and then tap the thermostat with the handle of a screwdriver, it may unfuse them. Check with the voltmeter again and see if you have 240 volts at the element. If not, change the upper thermostat.

          • #288225
            Avatar photoGuest

              To Elzo or fourth year: On a two element electric hot water heater, what should the delta be between the two thermostat settings & which one should be higher?

            • #288226
              Avatar photoJerry Peck

                Both thermostats should be set to 120 degrees.

                It takes over 5 minutes to get 2nd and 3rd degree from water which is 120 degrees.

                Water which is 130 degrees will produce 2nd and 3rd degree burns in about 30 seconds.

                Water which is 140 degrees will produce 2nd and 3rd degree burns in less than 5 seconds.

                Water which is 150 degrees will produce 2nd and 3rd degree burns in about 1 1/2 seconds.

                Water which is 160 degrees will produce 2nd and 3rd degree burns in about 1/2 second

                The above is from A. O. Smith literature and warning labels.

                It should also be noted that dishwashers which do not preheat the water (most do not) require water which is minimum 125 degree before any sanitizing begins. As shown above, water at 125 degree water is getting close to the critical 130 degree / 30 second scald time.
                [Edited by Jerry Peck on 13 October 2000]

              • #288227
                Avatar photoSylvanLMP

                  According to most HEALTH authorities and the better pluming codes
                  a dish washer operating temperature for DOMESTIC shall be 140-160 degrees and for Commercial 160-180 degrees for sterilization in lieu of chemicals.

                  This is one of the reasons why commercial heaters have a much higher temperature range and why Holby tempering valves and anti scald devices have been manufactured.

                  On my installations using the higher temperatures I run a dedicated line to the pot scrubber/dishewasher and temper the water for the rest of the building.

                  Most health authorities will agree 125 DOESN’T KILL all the bacteria. Have a nice day

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