Bad/dirty/corroded connection some where. If it's on both solenoids, that gives you a starting point as it's not on the 'downstream' side of either...
Look for a problem in the red wire circuits, or the grounds. Don't forget the control side either. If you have no power reaching the button panel, there's nothing to drive the solenoids. Especially if you aren't getting any clicking from the solenoids.
Start with a test light on the red wire coming into the panel. If it's too intermittent to be able to track with a test light (in this case I prefer a test light over a Multimeter, the light adds load that a meter doesn't), add a small diagnostic light to the panel. It should show power all the time. If the system doesn't operate, just look at the light. If it's still on, move down the circuit towards the solenoids...
This all assuming when it fails, it fails both UP and DOWN.....
Chris......
)
