F23
Saunier Duval
Flow/Return Temperature Differential Too High
Furnace displays F23, heating stops, may be accompanied by noisy operation
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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 partially blocked heat exchanger,Insufficient pump speed or failing pump,Closed radiator circuits,Incorrect system balancing
How to Fix / Troubleshooting
Safety first: Turn off power and gas before working on hydraulic components.
- Check pump speed: If the circulation pump has adjustable speeds, ensure it is set according to the system design. Increase speed if necessary.
- Open circuits: Make sure enough radiators or heating circuits are open to allow proper flow. Fully closed TRVs can cause excessive temperature differential.
- System balancing: Have a heating professional balance the system to ensure even flow through all circuits.
- Clean or descale: If the primary heat exchanger or filters are restricted, they must be cleaned or descaled by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Primary Heat Exchanger
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