Numerous fuel fired appliances have an igniter for igniting the fuel upon command.  Fuel fired appliances include, for example, heating, ventilation, and air conditioning (HVAC) appliances such as furnaces, boilers, water heaters, as well as other HVAC appliances and non-HVAC appliances.  Fuel fired appliances typically have a combustion chamber and a burner.  A fuel source, such as a gas or oil, is typically provided to the burner through a valve or the like.  In many cases, various electrical and/or electromechanical components are provided to help control and/or otherwise carry out the intended function of the fuel fired appliance.  For example, various controllers, motors, igniters, blowers, switches, motorized valves, motorized dampers, and/or others, are often included in, or are used to support, a fuel fired appliance. 
One particular type of fuel fired appliance is a fuel fired furnace.  Fuel fired furnaces are frequently used in homes and office buildings to heat intake air received through return ducts and distribute heated air through warm air supply ducts.  Such furnaces typically include a circulation blower or fan that directs cold air from the return ducts across metal surfaces of a heat exchanger to heat the air to an elevated temperature.  A burner is often used to heat the metal surfaces of the heat exchanger.  The air heated by the heat exchanger can be discharged into the supply ducts via the circulation blower or fan, which produces a positive airflow within the ducts. 
In some instances, the burner of the fuel fired appliance may fail to ignite the fuel during an ignition trial.  For safety and other reasons, many control systems for fuel fired appliances include a flame detector to detect the presence or absence of flame during or after ignition trials.  If the flame detector fails to detect the presence of a flame in the burner, the control system may shut down the burner, and in some cases, enter a lockout state.  Once in a lockout state, and in some cases, a service technician must be called to diagnose and correct the problem before the fuel filed appliance can return to an operational state. 
Under some circumstances, such as when the flame detector has become dirty or misaligned, the flame detector may not detect the presence of a flame, even though a flame exists.  This may require a significant amount of time for a service technician to diagnose the problem as it often results in intermittent operation of the appliance.