Kospel Overpressure / Expansion Vessel Failure

Safety relief valve on the furnace frequently 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

Failed expansion vessel diaphragm, Overfilled system, Faulty pressure reducing valve on fill line, Overheating due to control issues

How to Fix / Troubleshooting

Safety: Hot water discharge can cause burns. Do not cap or block the relief valve outlet.

  • Check system pressure: When cold, verify pressure is within Kospel's recommended range. If too high, bleed water from a drain point to reduce pressure.
  • Check expansion vessel charge (for qualified users): With system pressure at zero and isolated, measure the air charge at the vessel Schrader valve. Recharge to the specified pressure if low.
  • Inspect fill valve: Ensure the filling loop is fully closed and not letting water in continuously.

If the vessel will not hold charge or the relief valve continues to discharge, both may need replacement by a heating professional.

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Repair Difficulty

Hard 4/5

Required Part

Expansion Vessel
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