E20
Thermona
Condensate Drain / Siphon Fault
Boiler shows E20, burner stops, may be associated with condensate issues on condensing models.
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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 Thermona condensate trap or drain pipe, Frozen external condensate pipe, Incorrectly installed condensate pipework, Faulty condensate level sensor (if fitted)
How to Fix / Troubleshooting
Safety: Condensate is mildly acidic. Wear gloves and eye protection when handling.
- Check external pipe: Inspect the external condensate pipe for freezing (common in cold weather) or blockages. Thaw gently with warm (not boiling) water if frozen.
- Inspect trap (engineer level): Remove the condensate trap from the boiler and clean out any sludge or debris. Refill with clean water before refitting to maintain the water seal.
- Check pipe fall: Ensure the condensate pipe has a continuous fall to the drain and is not sagging or back-falling.
- Sensor check: If the boiler uses a condensate level sensor, inspect and clean it. Replace if faulty.
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Repair Difficulty
Medium
3/5
Required Part
Condensate Trap / Siphon
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