We report an incident involving a Fisher and Paykel “Three in One Respiratory Care System” (Fisher and Paykel Healthcare, Auckland, New Zealand). This is a new ventilator circuit designed to be adaptable to the needs of ventilator, intubated CPAP, and mask therapies. In this case the patient had received eight hours of CPAP therapy overnight, during which time the “Three in One” circuit had been broken down to the CPAP configuration. The expiratory limb heater element, normally disconnected, was inadvertently left connected to the heater base. Under the extreme conditions of heating under “no gas flow” mode, the heater element malfunctioned. As a result when the circuit was reconfigured to provide pressure-supported ventilation, in the high oxygen environment of the expiratory limb (FiO2 0.5), ignition and combustion of the respiratory circuit occurred. The case is reported because of the potentially serious consequences and because the incident prompted the manufacturer to redesign and change componentry in parts of the circuit implicated.