Hi all, thanks for the responses. So i isolated the valves last night, set to 1.5 bar and this morning 10 hours later it is still at 1.5 bar. I guess this means the problem is not in the boiler/system?
I also spoke to my tiler this morning and he does these jobs all the time and always applies the same process, so I am sure he has done the right thing here. Only last month he tiled a 400sqm car showroom in Liverpool and he used the exact same process as he did on mine.
I have spoken to a company which does thermal imaging and will look to get them out in the next few days to detect where the leak is, I will sadly then have to get my tiler back round to dig up that area, get the pipework fixed and retile over. The plumber at this company did mention it may be a faulty heat exchanger, but he said he'd come and take a look. I can't go back to the original company I used as the fella who owns it is going through a divorce and he will be dissolving the company 🙄