Vaillant Condensate Leak / Flue Condensate Backflow

Condensate dripping from bottom of boiler casing or staining on wall below flue

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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 condensate trap or pipe, Cracked condensate hose, Incorrect flue slope causing condensate to run back, Failed seal on condensate collector

How to Fix / Troubleshooting

Safety: Condensate is mildly acidic; wear gloves and eye protection. Isolate power before opening the boiler.

User checks:

  • Inspect the external condensate pipe for blockages or freezing; clear gently if safe.
  • Place a container under any visible drip to prevent damage.

Professional checks:

  • Remove and clean the condensate trap and internal hoses.
  • Inspect and replace any cracked condensate pipes or seals.
  • Verify correct flue installation and slope.
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Repair Difficulty

Medium 3/5

Required Part

Condensate Trap
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