Vaillant
Internal Water Leak
Boiler leaking water from underneath the casing
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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
Leaking automatic air vent, Corroded primary heat exchanger, Dripping pump housing or seals, Leaking pressure relief valve discharge inside casing
How to Fix / Troubleshooting
Safety: Switch off power and close the boiler’s isolation valves. Water may be hot; use caution.
- Identify leak source (visual only): Remove the lower cover (if user-accessible) and look with a torch to see where water is originating—top (heat exchanger/air vent), middle (pump/hydraulics), or bottom (PRV, condensate).
- Check pressure relief discharge: If water is coming from the pressure relief valve pipe, system pressure may be too high or the expansion vessel failed. Do not cap or block this pipe.
- Dry area and place tray: Place a container or towel to catch drips and prevent damage to flooring.
- Call a technician: Internal leaks require component replacement (e.g. air vent, pump seals, heat exchanger) and should be handled by a qualified engineer.
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Repair Difficulty
Hard
4/5
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