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The Goodman B1370189 Primary Limit Switch is a genuine OEM high-limit safety control for GMT090-5B gas furnaces. Mounted on the heat exchanger bulkhead, this primary limit opens at 200°F to interrupt the burners if the plenum overheats — a common protection against dirty filters, closed vents, and blower problems.
The B1370189 is set to the exact 200°F cutoff Goodman specified for this heat exchanger and plenum design. Because the primary limit is the furnace's main overheat safeguard, substituting a generic switch with a different set point risks either nuisance lockouts or inadequate protection. Use the genuine OEM part.
Rating: Easy (1/5). Replacement takes roughly 10–15 minutes with a nut driver. Cut power at the breaker before servicing. Remove the two wire terminals and mounting screws, then install the new switch in the identical orientation. If the limit had tripped, always confirm proper airflow — filter, ductwork, and blower — before returning the unit to service.