Main
Internal Water Leak
Boiler leaking water from underneath the casing or pipe connections
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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 pump housing or seals, Corroded primary heat exchanger, Dripping automatic air vent, Loose compression fittings on flow/return
How to Fix / Troubleshooting
Safety: Isolate electrical power immediately if water is leaking inside the boiler. Close the boiler flow/return isolation valves and the cold inlet (for combi models) to limit water loss.
- Identify leak source (visual only): Remove the front cover (if user-removable) and use a torch to see where water is originating—around the Main pump, heat exchanger, or fittings.
- Check pressure: Note the system pressure; a rapid drop indicates a significant leak. Do not keep topping up a leaking system.
- Tighten accessible joints: If you can clearly see a weeping compression joint on external pipework, gently tighten with appropriate spanners. Do not overtighten.
- Engineer tasks:
- Replace leaking pump seals or the complete Main pump assembly.
- Replace a corroded Main primary heat exchanger if pinholed.
- Renew the automatic air vent on the boiler top if it is dripping.
- Pressure-test the boiler and system after repairs.
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Repair Difficulty
Hard
4/5
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