Aqua valve not working

Hi growers, I have two autopot auto5 connected to a single 100L flexi tank. Everything has been working fine for the past 9 weeks but a few days ago I come to check the pots and they're completely dry. I lifted the valve and water started to run through (tried it separately on both trays) and they work fine when I manually lift the valve but when the trays are empty they have stopped refilling. I've checked all the pipes and they're fine, taken apart the auto valves, cleaned them and made sure the blue rubber stops are in the correct position too. I can't work out why they've stopped working.

Can anyone help?