ignition or start up this pocket of gas surrounds the ignitor ensuring that the gas comes in direct contact with the igniter and promoting a quick and complete ignition an electronic control circuitry is preferably protected within control box 64 the control box 64 is mounted on the top of housing 12 the electronic control circuitry includes an ignitor circuit switches relays for controlling the operation of the motor 20 the operation of the regulator 60 and the opening and closing of solenoid valves 54 56 a thermostat 66 and an on off switch 67 an ac power cord not shown provides electrical power to the control circuitry the control circuitry is similar to the control circuitry in other direct fired heaters and is a key element in the safe operation of the combustion system an important difference though is that the subject control circuitry includes circuits to allow the variable or gradual adjustment of the heater 39 s output the control circuit when signaled by the operator to start the combustion process activates the ignition circuit the ignition circuit and the solenoid valves 54 56 are activated beginning the flow of gas into the combustion system 50 and over the.