21
Immergas
DHW Modulation / Flow Regulation Error
Error 21; unit indicates domestic hot water flow rate or temperature regulation fault.
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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
Scaled plate heat exchanger, Sticking DHW modulating valve, Faulty DHW flow sensor, Incorrect parameter settings
How to Fix / Troubleshooting
Safety: Isolate power and close water valves before removing hydraulic components.
- Check inlet filters: Clean cold water inlet filters to ensure adequate flow.
- Descale plate heat exchanger: If hot water temperature fluctuates or drops at higher flows, the DHW plate heat exchanger may be scaled. Remove it and flush with an approved descaling solution, or have a technician perform in‑situ descaling.
- Inspect DHW modulating valve: On models with a motorized valve, ensure the actuator is connected and moves freely when hot water is demanded.
- Verify DHW flow sensor: Confirm that the flow sensor is clean and correctly installed.
Recommendation: Complex DHW modulation issues are best handled by an authorized Immergas technician with access to service parameters.
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Repair Difficulty
Hard
4/5
Required Part
DHW Plate Heat Exchanger
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