Saunier Duval
Chronic Pressure Loss
Boiler 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
Leak in central heating pipework or radiators, Faulty expansion vessel losing charge, Safety valve passing water, Micro-leaks inside boiler hydraulic block
How to Fix / Troubleshooting
Safety first: Allow the system to cool before inspecting for leaks.
Steps to check:
- Top up the system to 1.2–1.5 bar and monitor the gauge over several days.
- Inspect all visible pipework, radiator valves, and radiator panels for signs of dampness or staining.
- Check the safety valve discharge pipe outside for intermittent dripping.
- If pressure rises significantly when hot and then drops when cool, the expansion vessel may need recharging or replacement (engineer task).
- If no external leaks are visible, an internal leak within the boiler (e.g., plate heat exchanger) may be present and requires professional diagnosis.
Warning: Constant topping up introduces fresh oxygen and accelerates corrosion; do not ignore ongoing pressure loss.
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Repair Difficulty
Medium
3/5
Required Part
Expansion Vessel / Safety Valve
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