Is this the high-limit thermostat for my Samsung dryer?
Yes - DC47-00018A is the high-limit thermostat (L250). It is also included in the Samsung Heater Repair Kit with the element, thermal fuse, thermal cut-off and thermistor.
How do I test this thermostat?
Disconnect its wires and check it with a multimeter on continuity - testing it disconnected is the correct method. No continuity means it has failed.
My heating element failed. Do I need to replace this thermostat too?
No - only parts that test bad must be replaced. The Heater Repair Kit includes this thermostat plus the fuse, cut-off and thermistor, which is handy to keep on hand.
Why did my dryer stop heating again a few months after the repair?
A restricted vent is the usual cause. Make sure the exhaust vent is clear and clean the lint filter every cycle, then retest the fuses, thermostats and element.
Does this come with the ceramic block that holds the heating element terminals?
No - neither this thermostat nor the heater repair kit includes the ceramic terminal block. It only comes with the full heater housing assembly (DC97-14486A).