Temperature controller is flashing S.Br.
1. Thermal Couple is open or not connected.
2. A loose connection somewhere inside of the controller. A loose wire anywhere in the circuit will cause an S.Br indication.
3. Some furnaces like the Mellen three zone furnaces remain in the latched state until you hit the Page key, which is the left-most button. If you unplug the TC and plug it back in, the controller will indicate S.br.
Alternatively, if you connect the TC and cycle power on the controller, it will detect the TC connection and S.Br goes away automatically.