No "click" - likely "Stuck" either the seal or the plunger both causes require disassembling the solenoid from the base and cleaning.
If the plunger is stuck inside the solenoid, loosen it with a sharp tip screw driver - gently working around the plunger to free it. Clean the seal, plunger, and inside of solenoid with WD40 and fine/extra fine steel wool or a brass pot/pan scrubbing pad.
The stuck plunger is from water remaining in the solenoid (only partially drained after clean out)
Generic Herbicides are likely the cause of the seal sticking. Water soluble concentrates typically use emulsifiers to keep the product in suspension. Emulsifiers are wax/wax like agents that attract the chemical concentrate but repel other emulsifiers to stay dispersed evenly in water. Emulsifiers are also impact the cost of the chemical so cheaper concentrates use cheaper emulsifiers that tend to stick to everything and thus the sticky residue bonds other materials as well. Generic concentrates are effective at their job and costing with the trade off that cleaning intervals/intensities need to matched to the use and downtime intervals for smooth function.
