Brötje Expansion vessel failure / overpressure

Boiler pressure rises rapidly when heating and discharges water from safety valve

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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

Loss of air charge in expansion vessel, Ruptured expansion vessel diaphragm, Overfilled system, Faulty safety valve

How to Fix / Troubleshooting

Safety: Hot water may discharge from the safety valve. Allow system to cool before working on pressure components.

  • 1. Check cold pressure: When cold, system pressure should be around 1.2–1.5 bar. If higher, drain some water from a drain cock to correct.
  • 2. Test expansion vessel: With system pressure at zero and isolated, measure the air charge at the Schrader valve on the Brötje expansion vessel. Recharge to the specified value (often ~0.8–1.0 bar) with a pump.
  • 3. Check for water at Schrader valve: If water comes out, the diaphragm is ruptured and the vessel must be replaced.
  • 4. Safety valve: If the valve continues to drip after pressure is normal, replace the safety valve.
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Repair Difficulty

Hard 4/5

Required Part

Expansion Vessel
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