E18
Defro
Internal Control Board Overheat
Boiler displays E18, internal temperature rises abnormally, fan speed may be high.
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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 ventilation around Defro boiler casing, Fan not extracting combustion gases effectively, Faulty internal temperature sensor on Defro PCB, Excessive ambient temperature in boiler cupboard
How to Fix / Troubleshooting
Safety: Do not operate the boiler with covers removed except for testing by a professional.
- Improve ventilation: Ensure the Defro boiler has adequate clearance and that any cupboard vents are not blocked by stored items.
- Clean air paths: With power off, gently vacuum dust from around the PCB compartment and internal fans (if fitted), avoiding direct contact with components.
- Check fan operation: Confirm that the main flue fan runs at ignition and during operation. If not, see E07.
- Ambient temperature: If the boiler is installed in a very hot space (e.g., unventilated loft), consider improving ventilation or relocating heat sources.
- Persistent fault: If E18 continues, the internal temperature sensor or PCB may be defective and should be replaced by an authorized Defro technician.
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Repair Difficulty
Hard
4/5
Required Part
Defro main control board
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