Saunier Duval
Chronic Pressure Loss / Leak or Expansion Vessel Failure
Furnace frequently loses pressure and needs topping up
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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
Hidden leak in system pipework or radiators,Leaking pressure relief valve,Failed expansion vessel diaphragm,Micro-leaks in heat exchanger
How to Fix / Troubleshooting
Safety first: Do not repeatedly overfill the system above the recommended pressure.
- Check PRV discharge: Inspect the pressure relief valve discharge pipe outside. If it drips when the system heats, the PRV may be passing due to high pressure or debris.
- Expansion vessel test (technician): A professional can check and recharge the expansion vessel. If the vessel is waterlogged, it must be replaced.
- Leak detection: Visually inspect all accessible pipework and radiators. For hidden leaks, a heating engineer may use leak detection methods or pressure testing.
- Heat exchanger check: In rare cases, internal leaks in the heat exchanger can cause pressure loss and may require replacement.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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