Vmb1tc button locked


I am axperiencin g a problem with one sensor VMB1TS.
It is recognised; it is addressed by the VMB1TC, it is coupled with the VMB4RY and it seems in somehow working because the WMB1TCis reading its temperature.
The button is not locked (as VMB1TC says) and when pressed, the red led inside the sensor blinks, signalling that the button has been pressed.
So, it seems fine, but there is no yellow led turning ON on the VMB1TS once the button is pressed.

Does anyone know the reason of that?

I cannot use the Velbus link because the 7.1 does not talk with my board setup.

Thanks for an answer.