E18
Keston
Diverter Valve Position Fault
Boiler intermittently shows E18, particularly when switching between heating and hot water
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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
Sticking diverter valve, Faulty diverter motor/actuator, Sludge in valve body, Position microswitch failure
How to Fix / Troubleshooting
Safety: Isolate power and allow the boiler to cool before working on the hydraulic components.
User checks:
- Note whether the fault occurs when using hot water, heating, or both, and inform the engineer.
Engineer checks:
- Locate the Keston diverter valve assembly and check the actuator for correct movement during changeover between DHW and CH.
- Remove the actuator head and manually exercise the valve spindle; if stiff, clean or replace the valve body.
- Test any position microswitches or feedback sensors for correct operation.
- Flush the system and fit a magnetic filter if sludge is present to prevent recurrence.
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Repair Difficulty
Hard
4/5
Required Part
Diverter Valve Assembly
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