A system for determining a fault condition in an infusion system including an infusion pump (10) capable of infusing fluid from a primary container (14) and a secondary container (25), the secondary infusion line having a valve (28), the primary infusion line having a check valve (29), the system comprising:a pressure sensor (50) to measure pressure within the primary infusion line (16)a memory (80) for configured to store pressure related values anda processor (75) in communication with the memory (80) and responsive to the signals provided by the pressure sensor (50), the processor programmed to:sample the pressure signalsestablish a baseline pressure valuestore the baseline pressure value in the memoryoperate the infusion pump to increase the pressure in the primary infusion linesample the pressure signals after operating the pump to increase the pressure in the primary infusion linecompare the baseline pressure value with pressure values sampled after operating the pump to increase the pressure in the primary infusion line andprovide an alert that a fault condition exists if the latter sampled pressure value equals or is greater than a selected threshold pressure value.
