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Expansion Vessel / Pressure Relief Valve Issue
Boiler's pressure gauge rises rapidly when heating is on and may discharge water from the safety pipe.
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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
Failed expansion vessel diaphragm, Loss of expansion vessel charge, Faulty pressure relief valve, Overfilled system
How to Fix / Troubleshooting
Safety: Hot water may discharge from the safety pipe; keep clear of the outlet.
- Check cold pressure: When the system is cold, ensure the pressure is around 1.0–1.5 bar. If higher, drain some water from a radiator to reduce it.
- Observe hot pressure: If pressure rises above 3 bar when hot, the expansion vessel is likely not functioning correctly.
- Recharge vessel (qualified person): Isolate and drain the boiler, then recharge the expansion vessel via the Schrader valve to the specified pressure.
- Replace PRV if leaking: If the pressure relief valve continues to drip after pressure is normal, it should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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