An apparatus for applying negative pressure therapy to a wound, the apparatus comprising: a source of negative pressure configured to be in fluidic communication via a flow path with a wound dressing placed over a wound, the source of negative pressure configured to provide negative pressure under the wound dressing; a valve configured to control supply of positive pressure via the flow path to the wound dressing; and a controller configured to: operate the source of negative pressure to supply negative pressure via the flow path to the wound dressing, determine a pressure difference between a pressure under the wound dressing and a pressure setting, generate a control signal according at least to the pressure difference, and using the control signal, operate the valve to supply positive pressure via the flow path to the wound dressing so that the pressure under the wound dressing reaches the pressure setting; and characterised in that the controller is configured to operate the valve to supply positive pressure when the controller applies intermittent negative pressure wound therapy to the wound, and to output the control signal to the valve to operate the valve to vary an amount of positive pressure provided to the fluid flow path. a source of negative pressure configured to be in fluidic communication via a flow path with a wound dressing placed over a wound, the source of negative pressure configured to provide negative pressure under the wound dressing; a valve configured to control supply of positive pressure via the flow path to the wound dressing; and a controller configured to: operate the source of negative pressure to supply negative pressure via the flow path to the wound dressing, determine a pressure difference between a pressure under the wound dressing and a pressure setting, generate a control signal according at least to the pressure difference, and using the control signal, operate the valve to supply positive pressure via the flow path to the wound dressing so that the pressure under the wound dressing reaches the pressure setting; and characterised in that the controller is configured to operate the valve to supply positive pressure when the controller applies intermittent negative pressure wound therapy to the wound, and to output the control signal to the valve to operate the valve to vary an amount of positive pressure provided to the fluid flow path. operate the source of negative pressure to supply negative pressure via the flow path to the wound dressing, determine a pressure difference between a pressure under the wound dressing and a pressure setting, generate a control signal according at least to the pressure difference, and using the control signal, operate the valve to supply positive pressure via the flow path to the wound dressing so that the pressure under the wound dressing reaches the pressure setting; and characterised in that the controller is configured to operate the valve to supply positive pressure when the controller applies intermittent negative pressure wound therapy to the wound, and to output the control signal to the valve to operate the valve to vary an amount of positive pressure provided to the fluid flow path.