De Dietrich Overpressure / Safety Valve Discharge

Water heater is leaking from the safety valve discharge pipe

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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 on De Dietrich system, System overfilled, Faulty pressure reducing valve on cold inlet, Debris on safety valve seat

How to Fix / Troubleshooting

Safety first: Hot water discharge can cause burns. Do not cap or block the discharge pipe.

Step-by-step checks:

  • Check system pressure: Read the pressure gauge. If above recommended (e.g., >3 bar), the system is overpressurized.
  • Reduce pressure: Bleed water from a radiator or drain point to bring pressure back to 1–1.5 bar (for sealed systems).
  • Test expansion vessel: Gently tap the vessel; if it sounds full of water, the diaphragm may have failed.

When to call a professional: Expansion vessel charging or replacement and safety valve replacement should be done by a heating engineer.

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Repair Difficulty

Hard 4/5

Required Part

Expansion Vessel
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