What on earth are you putting the pressure to.
Should be 1 bar COLD, SO Switch it off, LET it go cold. Several Hrs, Or overnight.
Over pressure releases at 3 bar, Should never get to that, unless a problem. You should also NOT be able to close off the overflow. IT is A SAFETY FEATURE. IF you can, Who ever installed it needs to be shot.
The system WILL loose pressure, if the safety valve is dripping. Which it will if going above 3 bar.
SD
May 2012