I just had this same problem with my brand new Latissima premium and I fixed it by adjusting the water hardness setting. The yellow water warning light being constantly on means the machine thinks the water is too hard and the machine needs descaling. In my case, the machine just needed to learn how hard my water actually is. In the manuals that came with the machine you should have been given a ph testing strip and there are instructions in the user guide about how to adjust the water hardness settings. As soon as I did that, the yellow hard warning light immediately went off. In my case the water setting needed to be adjusted to the 7-14 ph setting. I'm attaching pics of the water hardness setting instructions from the manual.

Pretty sure the yellow light means your pod tray is full. I thought it was a blinking yellow light, but anyway pull the tray out dump the pods and see if the light shuts off. thanks,Hope this works.