A roll out sensor is just that, it senses excess heat and opens the circuit via a thermistor. There to prevent fires on some heaters. If we knew what heater the OP has it would help.
Roll out sensor......
That is a 'Thermal Fuse' that is OUTSIDE of the combution chamber
IF flame should blowback out of combustion chamber it should trip the 'thermal fuse' (burns out at 190*F----one shot device)
Atwood uses them. Suburban doesn't
That is completely different then the 'Flame sensing' which is done via flame rectrification (AC Current to DC Current) which involves the Spark Electrode and Circuit Board (Used by Atwood & Suburban)