Boiler loses pressure over time (sealed systems) and needs frequent topping up.

Safety first: Allow the system to cool before checking valves or joints. Do not over-pressurise the system.

• Inspect for visible leaks: Check all radiators, valves, and pipework for signs of water staining or damp patches.
• Check safety valve discharge: Look at the end of the safety valve discharge pipe outside. Any dripping indicates the valve is passing and may need replacement.
• Examine boiler internals: Remove the front panel and look for signs of dried water marks or corrosion inside the boiler.
• Test expansion vessel: A failed vessel can cause pressure swings and apparent loss. Check and recharge as described in the over-pressurisation fault.
• Leak detection: If no obvious leaks are found, a professional leak detection test may be required.