E13
Rheem
Exhaust Overheat / Heat Exchanger Overheat
Rheem tankless water heater shows E13 and shuts down with hot exhaust
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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
Blocked or undersized vent, Excessive scale in heat exchanger, Fan speed too low, Faulty exhaust temperature sensor
How to Fix / Troubleshooting
Safety first: Turn OFF power and gas. Do not operate the unit until the cause is corrected.
- Inspect vent system: Verify vent diameter, length, and fittings match Rheem specifications. Remove any obstructions at terminations.
- Check fan operation: Listen for normal fan speed. If the fan is slow or noisy, the combustion blower may be failing.
- Descale heat exchanger: Perform a full descaling flush to restore proper heat transfer and reduce exhaust temperature.
- Inspect exhaust sensor: Locate the exhaust thermistor and check wiring. Replace the sensor if damaged or out of spec.
- If venting is non-compliant: Have a licensed installer correct the vent configuration.
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Repair Difficulty
Hard
4/5
Required Part
Heat Exchanger
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