E17
Thermona
3-Way Diverter Valve Position Fault
Boiler displays E17, no heating, but hot water may still function (on combi models).
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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
Stuck Thermona 3-way diverter valve, Faulty diverter motor/actuator, Debris in valve body, Faulty position microswitch or feedback sensor
How to Fix / Troubleshooting
Safety: Isolate power and allow the boiler to cool before working on the hydraulic block.
- Check symptom pattern: If DHW works but heating does not (or vice versa), the diverter valve may be stuck in one position.
- Exercise the valve: Switch repeatedly between heating and hot water demands to see if the valve frees itself. Listen for the actuator motor moving.
- Visual inspection (engineer level): Remove the front cover and observe the diverter motor during mode changes. If it does not move, check its connector and supply.
- Clean/replace valve (engineer level): Drain the boiler as required. Remove the Thermona diverter valve head and inspect the valve spindle for stiffness or debris. Clean or replace the valve cartridge or complete assembly.
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Repair Difficulty
Hard
4/5
Required Part
3-Way Diverter Valve Assembly
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