Boiler frequently loses pressure over days or weeks, requiring regular topping up, but no obvious leaks are visible.
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.
Possible Causes
How to Fix / Troubleshooting
Safety first: Do not overfill the system above 2.0 bar. Repeated topping up introduces oxygen and can cause corrosion.
User checks:
- Monitor the pressure gauge when the system is cold and hot; if it rises above 2.5–3.0 bar when hot and then drops when cool, the expansion vessel may be faulty.
- Inspect visible pipework and radiators for damp patches.
Technician checks:
- Isolate and drain pressure from the boiler, then measure and recharge the expansion vessel to the correct pre-charge (typically around 0.8–1.0 bar).
- Replace the expansion vessel if it will not hold pressure.
- Check the safety valve for signs of discharge and replace if it does not seal.
- Pressure-test the system to locate hidden leaks.
Persistent pressure loss should be investigated to prevent damage to the boiler and system.
Repair Difficulty
Required Part
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