Loss of pressure

Help I recently had a new towel radiator fitted. Since having it fitted my boiler has been losing pressure over a period of about a week. I first thought that it was due to air in the system and that the new radiator had to settle in etc. The boiler has had a new air vent, thermistor, pressure gauge and water cock fitted. yet it still looses pressure. The piping is now under a tiled floor which I am reluctant to lift. I re pressurize to 1.2 bar and the prewssure gradually reduces, when the heating is on the presuure stays at about 2 bar. I bleed the radiators and there is still some air coming out of them.
The gas man put a leak and inhibitor fluid into the CH water and this has slowed down the decrease in pressure but has introduced two TRV\\\'s clanking. They are ok when fully on and OK when off but at midway they tend to clank away, causing a lot of noise.

Any advice on pressure loss and clanky TRVS
boiler is a gloworm express 80 combi

The water leak seems to be associated with the towel rail having been installed, so it's reasonable to assume that the leak is on the new pipework. The towel rail installer should be responsible for sorting that out. Internal leak sealer should really only be used as a last resort since it's likely to cause other problems in narrow waterways in the boiler.