The fuel fired heater comprises a burn chamber (7), a fuel feed (3), a blower (6), a control unit (11) and an ignition system (2). The optimum starting procedure is selected by the control to achieve the best change of correct burn with minimum burn products. After a failure to achieve a burn the fuel feed is stopped and the burn chamber is flushed with an increased air feed before retrying the starting cycle. The flushing period is between 30 and 60 secs. The control system monitors the operation of the heater and detects a failure to achieve a burn. It also detects a flame out and non standard burn conditions.
