E21
A.O. Smith Lower Element / Thermostat Circuit Fault

A.O. Smith electric water heater shows E21; lower portion of tank stays cold

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Failed lower heating element, Open lower thermostat, Loose wiring at lower element, Sediment covering lower element causing overheat

How to Fix / Troubleshooting

Safety: Turn off power at the breaker and confirm with a meter before servicing.

  • 1. Access lower components: Remove the lower access panel and insulation to expose the thermostat and element.
  • 2. Inspect wiring: Tighten all connections and look for burnt terminals.
  • 3. Test lower element: With wires removed, measure resistance across the element. Replace the element if it is open or shorted to ground.
  • 4. Check thermostat: Ensure the lower thermostat is set correctly and making good contact with the tank. Replace if it does not switch power when the tank is cool.
  • 5. Flush sediment: Drain and flush the tank to remove sediment that can bury the lower element and cause overheating.
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Repair Difficulty

Medium 3/5

Required Part

Lower Heating Element
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