If you have a two storey house chances are you may have an ensuite, powder room or bathroom upstairs.
These fixtures are all connected under the concrete slab of the second storey and drain into one pipe called a stack line, which then connects to your main house sewer drain underneath the grounds surface. The stack line is located usually boxed in, in a corner of a room or on the outside wall of the house with access openings at the bottom and top.
If your bathroom upstairs becomes blocked, that is the bath, basin, toilet, shower and whatever else is upstairs, all at once and downstairs bathrooms are fine then you have a problem with the stack line either at the top or bottom bends or the graded horizontal section joining to the main drain.
If the house is a recently new build common problems are: construction rubble eg brick and concrete down the drain that has built up at the bottom of the stack collecting paper or the horizontal graded section of pipe in the ground connecting the stack line to the main drain is damaged and broken.
For older builds depending on the piping material used, blockages can also be caused by too much paper, tree roots, corrosion and breakages.
If only one fixture upstairs becomes blocked this usually indicates that the stack line is fine and the problem lies within the individual branch lines coming off the main drain underneath the concrete slab.