E12
Sime
Main PCB / Control Board Fault
Boiler displays E12, may indicate communication or internal electronics fault, boiler unresponsive
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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
Internal PCB failure, Damaged low-voltage wiring, Power surge damage, Moisture ingress on PCB
How to Fix / Troubleshooting
Safety first: Isolate power before touching any internal electronics.
- Power cycle: Turn off the boiler at the fused spur for 2–3 minutes, then restore power. If E12 returns immediately, suspect the PCB.
- Inspect wiring: Check all low-voltage harnesses between the display, sensors, and main PCB for loose plugs or visible damage.
- Check for moisture: Look for signs of water leaks above the PCB (e.g., from the automatic air vent or pump unions). Any leak must be repaired before replacing the board.
- Replace PCB (engineer task): A qualified engineer should fit a new Sime-approved PCB, transfer any configuration links, and re-commission the boiler.
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Repair Difficulty
Professional Required
5/5
Required Part
Main Control PCB
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