Mine did the same thing a couple of times. Once, all I had to do was unscrew the part with the wire on it, and run some water through it, and it had a piece of crud in it that flushed out. Another time, disassembly and reassembly solved the problem. The other time, there was a hole/crack in the diaphragm. So, I would try unscrewing the actuator first. If that don't work, disassemble, examine and reassemble IF the parts look good. If you got a crack in the diaphragm, TAKE THE PARTS WITH YOU and go buy a rebuild kit or two. Match the parts you have to what's in the package. Handy to have a rebuild kit around, even if you find upon disassembly that it just had crud in it.
Oh, yeah. Remember to turn your water off first. Once you have unscrewed the actuator or disassembled the whole valve, turn your water on JUST A LITTLE to let any trapped crud flow out. Then either reassemble or install rebuild kit.
They ain't rocket surgery, and once you've done one of them, you'll do the next ones a lot faster and be able to diagnose problems.
Sometimes, you can just unscrew that actuator valve, (remember, you turned off the water, right?) run a little water through it, screw the actuator back on, and get lucky if it's just a piece of crud. WATCH OUT, it's easy to overtighten those screws in that PVC body and strip them.
Good luck.
Steve