A11
Nibe Overpressure in Cylinder / Safety Valve Activation

Display shows A11; water heater indicates high pressure or safety valve activation.

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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

Faulty expansion vessel (loss of charge), blocked expansion line, defective pressure relief valve, cold water inlet check valve causing thermal expansion with no relief

How to Fix / Troubleshooting

Safety first: Hot water under pressure can cause severe burns. Do not cap or block any safety valve discharge pipes.

This alarm is related to excessive pressure in the hot water system.

  • Step 1 – Check pressure gauge:
    • Read the system pressure gauge; typical cold pressure is around 1–3 bar depending on local regulations.
  • Step 2 – Inspect safety valve discharge:
    • Ensure the discharge pipe from the safety valve is not blocked or frozen.
    • Look for continuous dripping, which may indicate overpressure or a faulty valve.
  • Step 3 – Expansion vessel:
    • Locate the potable water expansion vessel connected to the Nibe cylinder.
    • Check the pre-charge pressure (with system depressurized) using a tire gauge; recharge with air/nitrogen to the value specified by Nibe.
  • Step 4 – Reset alarm:
    • After correcting pressure issues, reset the alarm via the control panel.
    • Monitor for repeated discharge from the safety valve.

If pressure continues to rise excessively, contact a qualified plumber or Nibe technician to inspect the expansion vessel and safety group.

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Repair Difficulty

Hard 4/5

Required Part

Potable Water Expansion Vessel
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