We had a new CH combi boiler installed 4 months ago, corrosion inhibitor was added to the water and everything seemed to have been done correctly. I was away for about a month and noticed the boiler pressure was ever so slightly lower than when I left it. I went round all radiators checking for air, nothing until I got to the towel rail. A lot of air came out of it and then suddenly nothing - not even water came out. Checked the boiler and pressure was down to zero, so I refilled it slightly and it shot back up to 1 bar almost instantly. Got any small amount of air left in the towel rail out again until I got water coming out. Since then I have been monitoring the boiler pressure for the past few days and it looks like it’s dropping but so slightly that I don’t know if I’m worrying about nothing. At the start the pressure dial was on/just above the 1 bar mark and 3 days later it’s every so slightly below the 1 bar. I’m talking less than 1mm difference at the outer side of the dial. The attached photo shows the difference, both taken a few days apart after the boiler has not been switched on for a while. If there was a leak in the pipework, even a pinhole leak - would there be a much more noticeable drop? I have checked the radiators for any wet spots at the connections but haven’t found anything.
I wouldn't worry too much at present. Just monitor pressure ,if it continues to drop there is a problem.