Rheem XE40T06ST45U1 Water Heater Problems & Error Codes — Overview
The Rheem XE40T06ST45U1 is a 40-gallon tall electric storage water heater with dual 4500-watt elements and electronic control. This model uses a red-blink fault code system: 1 blink for lower thermistor failure, 2 blinks for leak detection or shutoff valve error, 3 blinks for dry fire, 4 blinks for element wiring or ECO trip, and 5 blinks for control board failure. The most frequent service calls involve tripped high-limit switches, failed thermistors, and loose or corroded element wiring connections. Leak sensor nuisance faults and dry-fire codes during initial fill or after service are also common on units with electronic controls.
Most Common Problems on This Model
- 4 red blinks and no hot water Tripped ECO high-limit switch or loose element terminal wiring causing open circuit, reset the ECO button under the upper access panel and tighten all element wire connections.
- 1 red blink code Failed lower thermistor or broken thermistor wire, replace the lower thermistor sensor and check the harness for damage.
- 2 red blinks and unit shuts off Leak sensor detecting moisture in the pan or sensor circuit fault, dry out the leak sensor, check for actual leaks around fittings and the lower element gasket, and reset the control.
- 3 red blinks during startup Dry fire protection triggered because the tank was not fully filled with water before power-on, shut off power, open a hot tap to purge all air from the tank, then restore power.
- No heat and no error code One or both heating elements burned out, test each element for continuity and replace any open element.
- 5 red blinks Control board or power board internal failure, replace the electronic control assembly.
- Water not hot enough Failed upper thermistor reading incorrect temperature or upper element failure, test and replace the defective thermistor or element.
- Breaker trips repeatedly Shorted heating element grounding to the tank shell, test element resistance to ground and replace the shorted element.
Parts That Commonly Fail
| Part | Notes |
|---|---|
| Lower thermistor sensor | Amazon | Causes 1-blink code when failed, common on units over 3 years old |
| Heating element (upper or lower) | Amazon | 4500-watt dual elements, failure causes no heat or 4-blink wiring fault |
| ECO / high-limit switch | Amazon | Trips on overheat, usually resetable but replace if it will not reset or trips repeatedly |
| Electronic control board | Amazon | Causes 5-blink code, also controls leak detection and element relay logic |
Water-Heater Error Codes for This Model
These codes apply to this model line:
When to Call a Pro
Call a licensed electrician or plumber for any work inside the heater if you are not comfortable working with 240-volt circuits. Always shut off the breaker and verify zero voltage before opening any panel. If you see active water leaking from the tank itself (not fittings), the tank is done and needs replacement. If fault codes return after you reset the ECO or replace a thermistor, the control board or element relay may have failed and a tech with a meter and the Rheem diagnostic flow is the right call. Gas work does not apply to this electric storage model. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.