F21
Aquacomfort
EEPROM / Configuration Memory Error
Heater displays F21; may occur after lightning or electrical work.
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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
Corrupted control board memory, Incompatible replacement board, Electrical surge damage
How to Fix / Troubleshooting
Safety first: Turn off power before accessing the control board.
- Power reset: Remove power for several minutes, then restore. Sometimes memory errors clear on reboot.
- Check model configuration: If a control board was recently replaced, verify that jumpers or DIP switches are set correctly for your Aquacomfort pool heater model and gas type.
- Firmware/config reload: Some models allow reloading default parameters via a service menu; consult the service manual.
- Board replacement: If F21 persists, the control board’s memory is likely damaged and the board must be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Main Control Board
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