This is a picture of a flame rollout safety switch it will trip at a set temperature. The temperature set point of the rollout is designed to open when the flame is coming out the front of the burners

Possible heat exchanger has a hole or big crack.
Another possible cause is a combustion air intake pipe getting a plugged screen, Which will cause the room to work in A negative air pressure. Then air will be pulled in through the exhaust vent pushing flames out of heat exchanger and tripping the switch.
Between the wires the switch has a resettable button, but the cause of the problem should be found before leaving furnace. Never jump safety switch as it could cause property damage.

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