E10
State
High Exhaust Temperature / Flue Overheat
State tankless water heater shows E10; unit may lock out and require reset.
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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
Restricted exhaust vent, Excessive vent length or improper sizing, Scaled heat exchanger, Failed exhaust temperature sensor
How to Fix / Troubleshooting
Safety: Turn off power and gas. Do not operate with a suspected flue overheat condition.
- Inspect venting: Verify vent pipe size, length, and number of elbows match the State installation manual. Look for sags, dips, or crushed sections. Correct any improper venting.
- Check termination: Ensure the exhaust termination is not blocked by debris, snow, or vegetation.
- Descale heat exchanger: Perform a full descaling flush if scale buildup is suspected, especially in hard water areas.
- Exhaust sensor: Locate the flue gas temperature sensor on the exhaust outlet. Inspect wiring and mounting. Replace the sensor if damaged or out of spec.
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Repair Difficulty
Hard
4/5
Required Part
Flue Gas Temperature Sensor
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