A couple of things which I have experienced which might help. I was having a problem of pressure loss a couple of years ago and eventually found it to be a very small leak on the bottom thread of one of the radiators. To fix, this would normally mean a drain down and removal of the radiator but I solved it by getting a bottle of sealer from ScrewFix. It is designed for central heating systems and does not damage the other moving parts . This solved the problem and I have not had any trouble since.
Usually at the end of the Summer, I remove all the radiator thermostat valve heads and using a pair of pliers and spray lube work the pin back and fore to make sure they don't freeze up during the time the central heating is off. If the thermostat top is carefully removed, it can be replaced without loss of the settings.
This lockdown has caused quite a lot of problems. About 4 years ago, I had new triple glazed windows fitted and about two weeks ago, there was a loud bang when one of them failed. The curious thing is that the middle pane is broken and completely crazed where as both the outer panes are untouched. because of lockdown, we will have to wait for a repair. Luckily the window is safe and functional so I will have to wait for the report.