HFS-6 won't spray?

[Pit Viper]

On my way home yesterday, I noticed my system was kicking on, but no flow registered.
I went home, disconnected the line from the nozzles, and moved the jumper from Park to Test. The pump kicked on, and was running strong, but nothing was coming out the end of the line.

While the pump was still running, I loosened the line from the pump at the flow control module. Water started spraying out, so there's pressure right up to the module. Then I loosened the line from the module to the nozzles, but nothing came out. Any idea why it's not flowing through the module itself?