A18
Fondital Condensate Drain / Siphon Fault

Boiler shows A18, condensate may be visible around the base, unit may be noisy

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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 on Fondital condensing boiler, Frozen external condensate pipe, Incorrectly installed condensate pipework, Siphon not primed

How to Fix / Troubleshooting

Safety: Condensate is mildly acidic. Wear gloves and eye protection if handling. Turn off power before working near the boiler base.

User checks:

  • External pipe: Check if the external condensate pipe is frozen (common in cold weather). If frozen, thaw gently with warm (not boiling) water or a warm cloth.
  • Leaks: Place a container under any dripping to prevent damage and call a technician.
  • Reset: After thawing, reset the boiler once.

Technician actions:

  • Remove and clean the condensate trap / siphon on the Fondital boiler.
  • Check the condensate pipework for correct fall and secure connections.
  • Prime the siphon with clean water before restarting.
  • Inspect for corrosion or damage in the condensing heat exchanger.
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Repair Difficulty

Medium 3/5

Required Part

Condensate Trap
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