Refrigerant leak in Xsara Picasso

For a few months I have lost refrigerant because of the thermostat lid, I have changed the lid and the thermostat, and it continues to lose when the car is put at the normal march temperature. After the last change of lid (I have changed it twice, one bought it in a spare parts store and another in Citroen) no longer lost me by the base, now it does it because of the purge cap, it is well tight, but it is seen that by pressure or temperature the liquid comes out where you can, to see if anyone can guide me, this has become a matter of pride, I have to find out what happens.
Thanks for your help.

Tell me a thing your vehicle is heated, or it works normally, or the Tenperature marker indicates that the car is on the 90 degrees?

First apologize for not having answered before, I have not had access to the Internet during the weekend.
The car is maintained at a normal temperature, but logically when it indicates in the picture that I must fill in the refrigerant level, I do it, and it is silent that is missing water because the glass is empty apart from the characteristic tuffillo required by the water it pulls.
A question, how can I know if the thermostat opens or not, I understand that with heating it with a lighter you must open.
Thanks for your interest.

An more data pair. The electro turns on and the avitual time is working?
The hoses are very hard when it is hot?
The lower and upper radiator hoses when this temperature have the same temperature?
The spark plugs have grayless inlays?

The electro has not been able to work for a long time (I imagine that the fan) is also true that I do not let him warm up, in these conditions I try to walk as little as possible, I will try to leave it until it skips.
Of the two most accessible hoses one of 50mm that goes from the thermostat lid to the radiator, it remains almost cold and without pressure, the other that goes under this cover to the expansion vessel is very hot. The lower radiator I have not checked, I tell you in the afternoon.
As for the spark plugs, it is diesel and at least on the outside I do not see inlays.
To understand all this a little better, could you make an explanation in which direction the refrigerant moves?
Thank you