A low but steady pressure, with the same method, usually means a leak or less resistance in the path. Look for liquid at pump fittings, a loose column fitting, a worn pump seal, or a column that is not the one you think is installed. Also confirm the flow set-point and that the mobile phase composition has not changed.
Tighten a leaking fitting only until the leak stops. Over-tightening cuts ferrules and makes the next leak worse. If the pump runs and the pressure is near zero, treat it as “no pressure” below.
Call Mahut if the leak is inside the pump head, if seals have already been replaced once, or if tightening the visible fittings does not hold.