I had warramty work done on my Yamaha recently. I bought the piano about 400 miles from where I live. The dealer contacted Yamaha who gave them the name of their warranty repair contractor in my area, and then the dealer faxed a work order. After some delays for ordering parts, the tech came to my house, did the repair and that was that. (The problem had to do with a software bug that required replacement of the main circuit board.)
My understanding is that pretty much all manufacturers have arrangements like this with certified technicians who do not work for the company. Many of them do work on multiple brands. They are also the ones who do non-warranty work. I had one such call on my Roland, which I bought used and out of warranty. The service call was $100 or so. In both cases I was able to watch the tech take the piano apart, which will be helpful if I ever need to do minor things (like a blown fuse) myself.
Note that both of these pianos had "furniture" cases as opposed to being stage pianos, thus requiring a house call. Stage pianos can be taken directly to repair stations, and the warranties for them may not cover home visits.
Mason and Hamlin BB, Clavinova CVP900