Yes, the fuse is connected inline with the COM wire so all solenoids will go through the fuse since all are connected to the COM wire. I can’t explain the burn out. The circuit already has a number of protections in place: each zone has a RC snubber circuit to absorb sudden voltage/current changes, it’s protected by a TVS diode for transient high voltage, and there is an inline fuse on the COM wire. The fuse rating should be higher than 800mA because all triacs can sustain a quite high impulse current (up to several amps) in the event of transient high current. Generally, in the event of shorting, a very high amount of current would flow through the fuse, hopefully burning it out to protect the circuit. So exactly how the traic is burned, I don’t know. Is the expander completely unusable or is it that just the first zone is not?