A humidifier heater base assembly (6) is disclosed for use in a humidifier which is used for heating and humidifying a flow of respiratory gases supplied to a user. The assembly preferably includes a heater plate (44) having a thermally conductive portion and a perimeter portion around the perimeter of the heater plate, and a resilient member (40) having an inner part attached to the perimeter portion. An outer part of the resilient member is adapted to provide a resilient perimeter flange around at least part and preferably the whole of the perimeter portion. The resilient member is adapted to allow the heater base to be fixed to the humidifier by the resilient perimeter flange in such a manner that the heater plate and the inner part can move relative to the humidifier in a direction substantially transverse to the general plane of the heater plate. At least a portion of the resilient perimeter flange remains stationary relative to the humidifier.
