tile map service - Displaying/opening local TMS with QGIS

I want to display the content of a local TMS (a tile map, stored in a directory structure Z/X/Y.png) in QGIS.

This is for quick check and comparison. I am not willing to set WMTS webserver for this purpose.

I tried to load this kind of file in QGIS but I got only a white or stripped map

  
  
    file:///vdata/myTMS/${z}/${x}/${y}.png
     png
     TRUE
  

  
    -20037508.34
    20037508.34
    20037508.34
    -20037508.34
    11
    1
    1
    bottom
  

  EPSG:3857
  256
  256
   4   
     

I am running QGIS 2.14