The smell of a blocked urinal can be quite unpleasant. Flushing urinals will often block because of too excessive limescale build up in the urinal pipe.

This occurs as limescale is insoluble in water and forms on the pipe surface. When the urinal is descaled the pipe is cleaned to the base of the trap, however there is often more build up past the trap which cannot be cleaned. Partially degraded limescale can fall off the pipe wall and as it is soft, can block the drain.