Problems with pressurised central heating system

Hope someone can help.

With part of a major extension/rebuild of my house 4 years ago I had a pressurised central heating system. The one with a red and blue pressure containers by the hot water tank.

I have an ongoing issue with the pressure dropping to almost nothing quite regularly. I know that it needs redoing from time to time, but not as much as I do it!

So I have a few questions.

The overflow does operate from time to time and I don't know why?
Somebody said to me that the pressure valve on one of the coloured containers may be faulty?

There is evidence of some past weeping(copper pipe gone green) at the pipes connecting some of the radiators. Can I put an additive in to the system to cure these? If so where?

There is sometime major gurgling in the system that I assume is linked to the above?

Thanks

I would suggest that your expansion vessel probably requires recharging...any plumber can do this

Check the vessel against the system volumn , as youv`e added extra (rads)
What happens upon heat up is expansion which has to be accomodated by the vessel. With a cold start up make a note of system pressure on the gauge ABout 1.5 bar Turn on until full temp acheived , if there is a prob with the vessel the gauge will rise above 3 bar and the safety valve will pass if it does a re charge of the vessel or a larger one will be required.