E21
CTC
Diverter Valve Position Fault
Boiler displays E21; diverter valve not reaching position or stuck.
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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 cartridge, Faulty diverter motor/actuator, Debris in hydraulic block, Wiring fault to diverter motor
How to Fix / Troubleshooting
Safety: Isolate power and close water isolation valves. Allow the boiler to cool.
- Check symptoms: Note whether heating, hot water, or both are affected. Inconsistent switching between modes suggests diverter issues.
- Inspect actuator: Locate the diverter valve motor on the hydraulic block of the CTC boiler. Check for signs of water ingress or corrosion.
- Manual movement (technician): Remove the actuator and manually move the diverter spindle. If stiff or seized, the valve cartridge may need replacement.
- Replace actuator or cartridge: If the motor does not drive correctly or the valve is stuck, replace the diverter motor and/or valve cartridge according to CTC instructions.
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Repair Difficulty
Hard
4/5
Required Part
Diverter Valve Assembly
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