A breathing assistance apparatus that comprises a housing with inner and outer walls and an upper surface, wherein the walls and upper surface are integrally formed as a single part to avoid seams or joins between the walls to reduce the risk of damage to electronics within the apparatus as a result of liquid leaks. Also disclosed is a control system for a heating element of a humidifier which provides a secondary or back up protection mechanism to disable power to the heating element if a first electronic protection circuit does not cause the first switching member to disable power to the heating element.