A negative pressure wound therapy apparatus, comprising: a negative pressure source (150, 340) configured to be in fluid communication with a wound dressing configured to be positioned over a wound, the negative pressure source (150, 340) configured to provide negative pressure to the wound; a canister (220, 320) configured to be in fluid communication with the wound dressing and the negative pressure source, the canister configured to collect exudate aspirated from the wound; a pressure sensor (280, 282, 284, 330) configured to monitor one or more characteristics of pressure signals generated by the negative pressure source, the one or more characteristics of the pressure signals comprising magnitude of the pressure signals, the magnitude of the pressure signals increasing as a level of exudate in the canister increases; and characterized by a controller configured to: determine a leak rate of fluid in a flow path configured to fluidically connect the dressing, the canister and the negative pressure source based on a level of activity of the negative pressure source, and indicate the canister is full of exudate in response to determining that the pressure signal magnitude bounce satisfies one or more pressure thresholds corresponding to a value selected or determined based on the negative pressure setpoint and the level of activity of the pump; and further based on the determined leak rate. a negative pressure source (150, 340) configured to be in fluid communication with a wound dressing configured to be positioned over a wound, the negative pressure source (150, 340) configured to provide negative pressure to the wound; a canister (220, 320) configured to be in fluid communication with the wound dressing and the negative pressure source, the canister configured to collect exudate aspirated from the wound; a pressure sensor (280, 282, 284, 330) configured to monitor one or more characteristics of pressure signals generated by the negative pressure source, the one or more characteristics of the pressure signals comprising magnitude of the pressure signals, the magnitude of the pressure signals increasing as a level of exudate in the canister increases; and characterized by a controller configured to: determine a leak rate of fluid in a flow path configured to fluidically connect the dressing, the canister and the negative pressure source based on a level of activity of the negative pressure source, and indicate the canister is full of exudate in response to determining that the pressure signal magnitude bounce satisfies one or more pressure thresholds corresponding to a value selected or determined based on the negative pressure setpoint and the level of activity of the pump; and further based on the determined leak rate. determine a leak rate of fluid in a flow path configured to fluidically connect the dressing, the canister and the negative pressure source based on a level of activity of the negative pressure source, and indicate the canister is full of exudate in response to determining that the pressure signal magnitude bounce satisfies one or more pressure thresholds corresponding to a value selected or determined based on the negative pressure setpoint and the level of activity of the pump; and further based on the determined leak rate.