Pressure loss sealed system

[Grantplant]

Hi looking for problem solving here please.

I have a megaflow. Was fine until works done on cylinder, pipework altered.at same time I had works done by builder on garage conversion including running new pipework part of which is under tiled floor now. .over last volume of months I keep loosing pressure . No heating on only water. Pressure seems to hold sometimes for a couple of weeks then just goes. I topped up last night to 1 bar. By 9 am this morning pressure gone, checked boiler pipe outside and completely dry no dripping.

It seems to be so inconsistent I just cant work it out. Cant not see any leaks anywhere but it is too much of a coincidence work carried out and started happening.

I have two pressure guages one on boiler. I have shut of flow and return at boiler to keep independent under pressure to see if pressure drops. Nothing yet.

The second guage is in the airing cupboard by the cylinder. I will check this kne also to see if this drops. Again nothing yet.

Looking for suggestions please I dont want to rip up floor only to find ok

 

[Ltnman]

I had a leak 12 years ago that could not be found. This fixed it https://www.toolstation.com/fernox-...8A_4jj_qyedCHNOLRshoCSE0QAvD_BwE&gclsrc=aw.ds

 

[Grantplant]

ok so no pressure loss overnight from boiler or rest of system with boiler turned off. Running off cylinder element to get hot water at mo mains fed. Any ideas . It seems intermittent?