How often do you depressurise your LDS system?

[osx]

It seems that over time pressure builds in the system (I can usually feel the suspension getting a bit more firm) and when I remove the LDS cap there is a hiss. This weekend it was really bad (temperature related?) and will depressurise the system with the Lexia. Why would pressure build up in a closed system?

[EDC5]

I believe the pressure in the reservoir is due to the changing volume of fluid in the suspension circuit. This changes with the ride height as the struts will be extended different lengths.

I can't see how pressure in the reservoir would affect the ride firmness as they are separated by electro valves.

This weekend it was really bad (temperature related?)

Do you mean the suspension is really stiff currently? if so it might be a good idea to check your ride height. Recently mine was riding about 4 or 5 cm too high and the ride was really harsh!