E18
Pennco
Return Temperature Too Low / Condensation Protection
Boiler display shows E18 and burner output is limited
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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
Oversized boiler with low return temperature, Mixing valve stuck open, Bypass valve misadjusted, Faulty return temperature sensor
How to Fix / Troubleshooting
Safety first: Use caution around hot piping.
- Check system design: Verify that the system has proper boiler bypass or mixing to maintain minimum return temperature as specified by Pennco.
- Inspect mixing/bypass valves: Ensure manual or automatic mixing valves are not stuck fully open, which can keep return water too cool.
- Verify sensor: Confirm the return temperature sensor is properly installed and reading correctly.
- Adjust controls: If the boiler has adjustable minimum return temperature settings, verify they are set per the installation manual.
- Consult a designer/technician: Persistent low return temperatures may require piping or control changes to protect the heat exchanger.
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Repair Difficulty
Hard
4/5
Required Part
Boiler Bypass / Mixing Valve
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