Electric water heaters use two surface-contact thermostats clamped against the outer tank wall at the upper and lower element positions. The upper thermostat serves dual duty: it controls the upper heating element and houses the ECO (Energy Cut-Off) safety switch that trips at approximately 170 degrees F, cutting power to both elements if the thermostat malfunctions and allows the water to overheat. Camco thermostats are universal replacements fitting Rheem, AO Smith, Bradford White, State, Reliance, Richmond, and most other residential brands.
Upper vs. lower thermostat
- Upper thermostat with ECO ($15-25): Controls the upper element and contains the red-button ECO reset. In a standard dual-element setup, the upper thermostat heats the top half of the tank first, then transfers power to the lower thermostat to heat the lower half. A tripped ECO (requiring manual reset) indicates the tank overheated -- investigate why before resetting.
- Lower thermostat ($10-20): Controls the lower heating element only. Receives power from the upper thermostat when the upper zone reaches set temperature. Failure of the lower thermostat causes poor recovery -- the tank heats the top half only and feels like it has reduced hot water capacity.
Thermostat failure symptoms
- Water is too hot or too cold despite correct temperature dial setting
- Only limited hot water available before it runs cold (lower thermostat failed)
- ECO tripped (red button popped out on upper thermostat) -- tank overheated
- No hot water at all (upper thermostat failed, cutting power to both elements)
Testing a thermostat
- Turn off the circuit breaker and verify zero voltage with a non-contact tester.
- Access the thermostat through the element access panel -- remove insulation and the protective plastic cover.
- Set a multimeter to continuity mode and probe the thermostat terminals with the dial set to 120 degrees F.
- A functional thermostat at room temperature should show continuity (closed circuit) across the element output terminals when set above ambient temperature.
Replacement
Disconnect the wires (photograph the terminals first), press the retaining clips to release the thermostat from the tank wall, and snap in the new Camco thermostat. Reconnect wires per the photograph and restore power.
Cost
- Upper thermostat with ECO: $15-25
- Lower thermostat: $10-20