Compare the reading with your usual pressure for the same column, flow, mobile phase, and temperature. A rise usually means a restriction: inline filter, guard column, column inlet frit, or plugged tubing. Buffer salts that have precipitated are a common cause.
Stop the flow before you open any fitting. Remove or bypass the guard column first and check the pressure again. If it is still high, stop the flow, remove the analytical column, and connect the inlet and outlet tubing with a union rated for the pressure. At the method flow, pressure with no column should fall to a low value set by the tubing. If it does, the restriction was the guard or the column.
If pressure stays high with the column out, isolate one section at a time, working back from the detector toward the pump. Do not backflush a column unless the column instructions allow it. Do not switch a salty aqueous system straight into a strong organic solvent; wash with a high-water mobile phase first.
Call Mahut if pressure is still high after the column is removed, if a fitting leaks or is damaged, or if you are not sure which solvent is in the pump.