CTC Expansion Vessel Failure / Overpressure

Boiler pressure rises rapidly when heating and the pressure relief valve discharges water.

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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

Flat or ruptured expansion vessel diaphragm, Blocked connection between vessel and system, Overfilled system, Faulty pressure relief valve

How to Fix / Troubleshooting

Safety: Allow the system to cool. Hot discharge water can cause burns.

  • Check cold pressure: When cold, ensure the system pressure is not above the recommended value (typically 1.0–1.5 bar). Drain some water if overfilled.
  • Expansion vessel test (technician): Isolate the boiler, drain pressure to zero, and measure the vessel air charge. Recharge to the value specified by CTC or replace the vessel if water comes from the Schrader valve.
  • Check vessel connection: Ensure the pipe between the expansion vessel and system is not blocked.
  • Replace PRV (technician): If the PRV has discharged repeatedly, replace it to ensure reliable sealing.
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Repair Difficulty

Medium 3/5

Required Part

Expansion Vessel
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