E03
Klimosz
Flue Gas / Exhaust Fan Fault
Boiler shows E03 and will 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 chimney on Klimosz boiler installation, Faulty flue gas fan, Defective air pressure switch, Blocked air intake or condensate trap
How to Fix / Troubleshooting
Safety: Turn off power and allow the boiler to cool. Risk of carbon monoxide – ensure good ventilation.
- Check flue and air intake: Inspect the flue terminal outside for obstructions (ice, leaves, bird nests). Ensure the air intake (for room-sealed Klimosz models) is not blocked.
- Inspect condensate trap: Remove and clean the condensate trap and hoses. Sludge or ice can block condensate flow and affect fan/pressure readings.
- Check fan operation: With power off, spin the fan wheel by hand through the inspection opening. It should rotate freely without scraping. Clean dust and debris from the fan blades.
- Inspect air pressure switch tubing: Check silicone tubes from the fan to the air pressure switch for cracks, kinks, or water inside. Replace damaged tubes and ensure tight connections.
- Test run: Restore power and call for heat. If the fan does not start or E03 persists, the fan motor or pressure switch likely needs replacement by a Klimosz service technician.
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Repair Difficulty
Hard
4/5
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