E03
ACV
Flue Gas / Air Pressure Switch Fault
Boiler shows E03 and does not start, fan may run briefly then stop
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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 flue or air intake, Faulty air pressure switch, Blocked fan venturi or tubes, Faulty fan
How to Fix / Troubleshooting
Safety first: Turn off the boiler and allow it to cool. Do not operate the boiler with a suspected flue blockage.
- Check flue terminal: Go outside and inspect the ACV boiler flue terminal. Remove any visible obstructions such as leaves, nests, or snow. Ensure the terminal guard (if fitted) is not clogged.
- Check air intake: On concentric flue systems, ensure the air intake annulus is not blocked. For separate air intake pipes, verify they are not obstructed.
- Reset the boiler: After clearing any obvious blockage, reset the boiler and see if E03 clears.
- Do not bypass safety devices: Never bridge or bypass the air pressure switch. If the error persists, a technician must test the air pressure switch, silicone tubes, fan speed, and venturi on the ACV combustion assembly.
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Repair Difficulty
Hard
4/5
Required Part
Air Pressure Switch
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