Products Affected: Modulating Gas Furnaces – (F,G)CMN Major Series B

Situation: Carrier has received increased reporting of nuisance limit trips and limit lockouts with our Major Series “B” modulating furnaces.

Solution: Carrier Engineering has previously updated intermediate Airflow values to reduce the likelihood of nuisance limit trips (see TIC 2025-0012 Modulating Furnace Airflow Updates). To further increase operational robustness, and further reduce the likelihood of nuisance limit trips, Carrier Engineering has re-tested and certified new limit switch values for the modulating furnaces. These updated switches will be introduced into production of the subject model furnaces, serial # 2547A and later. Subject model furnaces, produced prior to the manufacturing change date may be fitted with the newer, higher rated limit switches. The new limit switch part numbers MAY NOT be used to replace limit switches in the previous Major Series A modulating furnaces.

See full bulletin for replacement limit switch part numbers.

See previous bulletin TIC2025-0012 for airflow updates.