E10
Keston
Expansion Vessel / System Overpressure Fault
Boiler displays E10, system pressure rises rapidly when heating, safety valve may discharge
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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, Vessel lost charge, Blocked connection to vessel, Faulty pressure relief valve
How to Fix / Troubleshooting
Safety: Hot water and steam may discharge from the safety pipe. Do not cap or block the discharge pipe. Allow system to cool before working on it.
User checks:
- Note the pressure when cold and when hot. If it rises above 3 bar and the boiler shows E10, an expansion issue is likely.
- Do not keep topping up the system repeatedly; this can cause corrosion.
Engineer checks:
- Isolate the boiler from the system, drain pressure to zero, and measure the expansion vessel pre-charge via the Schrader valve. Recharge to the value specified by Keston (typically around 0.8–1.0 bar) or replace the vessel if water comes out of the valve.
- Check the pipe or hose connecting the vessel to the system for blockages or isolation valves that are closed.
- Inspect and test the 3 bar pressure relief valve; replace if it fails to reseat or drips continuously.
- After repairs, refill and bleed the system, then verify stable pressure during operation.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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