ch pressure probs

[680312]

ive got an ideal combi boiler that keeps losing pressure.
this happens when the boiler is not running.
there are no leaks and the prv is not discharging.
i switched the boiler off and it held its pressure.
i'm running it at the moment and the pressure is stable it just seems to happen when it is not running.
has anyone got any ideas?

 

[MANDATE]

Sorry can't agree, there's got to be a leak. The leak may only occur when pressure is high. ie when water has expanded. When water has contracted in volume and cooled, pressure drops and leak stops.
Does that not make sense?

 

[680312]

there's definitely no leaks,got floorboards up and system running.
i have noticed that when the boiler heats the water for storage the gauge for the ch moves slightly.could this in anyway affect this?