Diode case with black band in the middle

I have faulty High Powered Battery Fence Energiser PCB.
On the circuit board there is a diode case component with wide black band in the middle marked as Unknown component on the picture, linked with S2800D Gate. I measured unknown component across with multimeter and it is in 'Open' state. Can it be faulty zener diode? If yes, how then to find the right value without circuit diagram ?

Can somebody help me to identify unknown component on the circuit board?