Anthony Curren
If your boiler is constantly losing pressure the first thing to check is the pressure relief valve outlet this is outside the house near the boiler ( copper tube 15mm folded back to the wall ) if this tube is dripping it means that the pressure relief valve the expansion vessel or both are faulty. If when you run heating gauge on boiler goes above 3 the expansion vessel is faulty. If the pipe outside is constantly dripping the pressure relief valve is faulty. The other possibility is that a radiator leaks when hot and the water evaporates try wrapping valves in kitchen roll this will collect evaporating water and show.
