The Rheem tankless water heater is a compact, energy-efficient option for many American homes. When a fault code appears, it signals a specific issue affecting performance or safety. This guide explains common troubleshooting codes, how to read them, and practical steps you can take to restore hot water while emphasizing model-specific manuals for accuracy. Understanding these codes helps homeowners save time and avoid unnecessary service calls.

Common Error Codes And Their Meanings

Rheem tankless models use LED indicators or a digital display to signal faults. While codes vary by model, several codes recur across many Rheem units. The list below highlights typical interpretations. Always confirm with your model’s manual, as exact codes and procedures can differ between series.

E01 – Water Flow Issue: Low flow or sensor jam. Check for closed valves, clogged filters, or scale buildup.
E02 – Overheating: Water leaving the unit exceeds safe temperatures. Inspect for restricted venting, blocked intake, or improper gas pressure in gas units.
E03 – Ignition Or Flame Sensor Fault: Ignition not sustaining a flame or sensor misreading. Clean flame sensor and verify proper ignition sequence.
E04 – Pressure Switch Problem: Air pressure or water pressure abnormality. Verify water supply pressure and clear any air pockets in lines.
E05 – Ignition Failure: Repeated failed ignition attempts. Check gas supply (for gas models), electrical connections, and ignition electrode condition.
E06 – Condensation Or Drain Issue: Excess moisture or improper drainage causing a fault. Inspect condensate line and ensure proper slope and clearance.
E07 – Sensor Or Board Fault: Sensor readings out of range or circuit board malfunction. Often requires professional inspection or board replacement.
E08 – Water Temp Sensor Fault: Sensor not reading accurately, causing incorrect temperature regulation. Replace sensor if needed and verify wiring.
E09 – Exhaust Or Vent Fault: Venting obstruction or improper vent configuration. Clear obstructions and confirm vent sizing and termination.

How To Read And Interpret Codes

Interpreting the codes begins with noting whether the display shows a specific number, a combination of letters and numbers, or blinking lights. Some models flash a sequence that maps to a code, while others display a numeric error. Once you identify the code, consult the user manual’s fault-code section for the precise meaning and model-specific actions. If the code persists after initial checks, record the exact sequence, model number, and operating conditions to aid professional service.

Useful steps before blaming the device include confirming power supply status, gas line availability (for gas units), water inlet pressure, valve positions, and the cleanliness of filters and heat exchangers. A clean, well-ventilated installation with clear intake and exhaust paths reduces many common errors.

Step-By-Step Troubleshooting These Codes

The following steps cover the most frequent issues associated with the codes above. Always turn off power and shut off gas supply (for gas models) before performing any maintenance. If uncomfortable with any step, contact a professional.

E01 – Check flow: Open all hot-water taps briefly to purge air. Inspect inlet strainer and filter for debris; clean if present. Ensure main supply valves are fully open and there are no downstream restrictions.
E02 – Overheating: Verify proper venting clearance and free airflow around the unit. Inspect water temperature settings; ensure the unit is not set above safe limits. Check cooling flow if applicable and confirm the heat exchanger is not scaling up with mineral buildup.
E03 – Ignition/Flame Sensor: Power cycle the unit to reset the control board. Clean the flame sensor with a soft brush or cloth; inspect the spark electrode for corrosion or misalignment. Confirm gas supply pressure is within manufacturer specifications if on a gas model.
E04 – Pressure Switch: Relieve any trapped air by bleeding the lines. Check the drain valve and ensure the pressure switch tube is connected and not kinked. Inspect water pressure from the supply and consult the flow curve in the manual.
E05 – Ignition Failure: Confirm electrical connections to the ignition system are secure. For gas models, verify the gas valve opens reliably during ignition; check for gas supply leaks and line integrity.
E06 – Condensation/Drain: Inspect the condensate drain for clogs or kinks. Ensure the drain is pitched correctly and that any pump (if installed) runs properly. Clear the path and re-test.
E07 – Sensor/Board Fault: Perform a full reset by powering off, waiting 60 seconds, and powering back on. If the fault recurs, a faulty sensor or control board may require replacement by a technician.
E08 – Water Temp Sensor: Check sensor wiring for loose connections. Replace the sensor if the readings remain erratic after reseating connections. Recalibrate as per the manual, if supported.
E09 – Vent/Exhaust: Inspect vent for blockages, ensure joints are sealed, and verify correct vent length and diameter per specification. Remove obstructions and retest for proper exhaust flow.

When To Call A Pro

Some issues exceed DIY scope, particularly gas supply irregularities, persistent flame-sensing problems, or suspected control-board failures. If a fault code reappears after performing the standard checks, or if there is water leakage, inconsistent flame, or persistent overheating, professional service is advised. A licensed technician can verify venting integrity, gas pressure, electrical safety, and circuitry with calibrated testing.

Maintenance Tips To Prevent Troubles

Regular maintenance helps minimize the occurrence of error codes. Routine actions include cleaning the inlet filter every few months, inspecting and clearing the condensate line, checking venting for obstructions, and scheduling annual professional inspections. Keeping the unit away from dust, chemicals, and high-traffic areas reduces accidental damage and sensor contamination. Document model numbers, serial numbers, and maintenance dates for quick reference during troubleshooting.

Model-Specific Notes And Resources

Because Rheem tankless models span residential and commercial lines, codes and procedures differ. Always consult the exact manual for the specific model and series. Online resources from Rheem’s official site, reputable plumbing forums, and local distributor guides can provide model-by-model fault-code maps. If a code is unclear or the manual is unavailable, contact Rheem customer support with the model number, serial, and installation date to obtain accurate guidance.