Vaillant
Chronic Pressure Loss
Vaillant boiler frequently loses pressure over days or weeks
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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
Small leak in heating circuit, Faulty expansion vessel, Weeping pressure relief valve, Micro-leak in primary heat exchanger
How to Fix / Troubleshooting
Safety: Do not repeatedly overfill above recommended pressure; this stresses components.
User actions:
- Top up system to correct pressure and monitor the gauge daily.
- Check visible pipework, radiators, and boiler underside for signs of damp or staining.
- Observe the PRV discharge pipe outside for drips when the system is hot.
Professional actions:
- Test and recharge or replace the expansion vessel.
- Replace a leaking PRV.
- Use leak detection methods (dye, pressure test) to locate hidden leaks.
- Inspect the primary heat exchanger for internal leaks into the combustion chamber or condensate.
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Repair Difficulty
Hard
4/5
Required Part
Expansion Vessel
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