IVT Expansion Vessel Failure / Overpressure

Boiler pressure rises rapidly when heating is on and discharges water from the 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

Flat or ruptured expansion vessel diaphragm, Incorrect pre-charge pressure, Blocked connection between vessel and system, Faulty pressure relief valve

How to Fix / Troubleshooting

Safety: Hot water may discharge from the safety pipe. Keep clear of the discharge outlet. Allow system to cool before working on it.

Steps:

  • Note the cold pressure (system off) and the hot pressure (system on). A large increase suggests expansion vessel issues.
  • A technician should isolate and check the expansion vessel pre-charge with a tyre gauge, recharging with air/nitrogen to the value specified by IVT (typically around 0.8–1.0 bar).
  • If the vessel will not hold pressure, replace the expansion vessel.
  • After repeated discharges, the pressure relief valve may not reseal properly and should be replaced.
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Repair Difficulty

Hard 4/5

Required Part

Expansion Vessel
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