I would suggest at least pull one wire out so you can see if that zone can at least run one valve. If you have any spare zone, you can consider combining two zones into 1 to support two parallel valves. This does not require you to set up a complete new wires, instead, you insert one wire to zone x, the other to zone x+1, and you can set one of them (say zone x+1) as parallel (i.e. turn off ‘sequential’ flag). Then schedule both of them in a program. This way, the two run at the same time, so logically still one zone, but since they are one two separate triacs, the current capacity is doubled and should drive two solenoids successfully.