Under certain circumstances, it is possible to damage the Stationary Phase Particles (dropping the Column on a hard surface, pressure shock etc) such that they would be comparable in size to the frit pore size.

This would then produce a high Column pressure due to the partially blocked flow area. Some of our Cogent TYPE-C™ Silica HPLC Columns are made with a 4um Particle and the frits used are 2um. In this case, the particles could get stuck in the Frits and produce high back pressure.

Sometimes running these columns in reverse direction on your HPLC will disslodge the particles and a proper flow will return.