The pressure drops to nothing on our combi boiler within an hour of pressurising it. The plumber says it is because we have a leak somewhere in the house but we can't find one. He says that there is at least a kettle full of water being lost somewhere in the house for the pressure to go down as fast as that. He now says the best thing to do is to replace all pipework in the house for over £1,000! Isn't there some equipment find the leak? Thanks, Sue

Of course that much water should just be noticeable if you look.
And are there shut off valves at various places who that you can shut off areas and see if it still drops.
There are machines that listen for the sound of leaking water ( not all will have that) And assuming this is hot water, there are themo heat detectors that will show variation in heat around windows and in walls.

But against if the entire system is old, perhaps it is dozens of small leaks so it is not as noticeable.