Apparatus (10, 200, 400) and methods for alerting a user of topical negative pressuretherapy apparatus to a non-flow condition of aspirant fluid in the apparatusare described, the apparatus comprising: a device (32, 202) having vacuum pumpmeans (44, 248) and a waste canister (22, 204) connected to the device； the wastecanister being operably connected to a wound dressing (14) by aspiration conduitmeans (12, 274) for aspirating fluid from the wound； the aspiration conduit means,the waste canister and the device providing a fluid flow path therethrough andthe vacuum pump means providing for fluid flow therethrough； the device havingfirst pressure sensing means (46, 402) at an upstream position between an outletport (28, 268) for aspirated fluid from said waste canister and said pump means；said waste canister having further provision selected from one of, selectablevent means (406) for admission of ambient air to said waste canister and selectablesecond pressure sensing means (422) for sensing pressure in said waste canister；and, a control system for receiving signals from said sensors and initiatingcontrol signals in response and activating an appropriate user alarm.
