Pressure loss

worcester 35cdi combi boiler has been losing pressure for 12 months now gradually getting worse,need now to add water every day ,had a new PRv fitted and new bypass adjuster screw fitted have bled all radiators many times but still pressure drops. I have no signs of any water leaks have pulled up floorboards/carpets had 3 plumbers out but they all say the same \\\"needle in a haystack\\\" must be a leak somewhere when i find it call them out and they will fix it! BUT I HAVE NO LEAK HELP!!!!

I have read that Fernox leak sealer can help in some cases. Might be worth a try

Have you used fernox yourself,Is it easy to apply or will I need a Plumber to use this product?

you can inject leak sealer via a radiator bleed point, the package comes with good instructions so you should be grand

good luck