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The Goodman B1370155 auxiliary limit switch is a genuine OEM secondary overheat control rated at 120°F for the GMTH090-5B gas furnace. Typically mounted on the blower housing, this auxiliary limit provides backup protection against heat buildup in the blower compartment — for example when airflow is restricted or the primary limit is slow to respond — by opening the control circuit to stop the burner.
The OEM B1370155 matches the 120°F setpoint and blower-mount geometry Goodman designed for this model. Generic auxiliary limits with different trip points can cause intermittent no-heat calls that are difficult to diagnose. For consistent, correct protection, OEM is the recommended fit.
Rated Easy — disconnect two leads, remove one or two screws, and swap. Shut off power at the disconnect before servicing. Confirm the blower and filter airflow are clear so the new switch isn't tripped by a real airflow problem.