Water not pumping through brush head

I have a diy wfp trolley it has been working fine for about a month. It has a Pentair shurflow pump 5.3 lpm a basic flow controller a battery and I have a flow tap on my hose now water will not pump through the brush head the pump 

Is working but no water is coming through the pole. The flow tap doesn't seem to be working because when I turned the flow tap off it would stop the pump this isn't working now. When I have had this issue before I have disconnected the pole hose from the brush turned it on put flow controller to the max and it has cleared the airlock but that isn't working. any help much appreciated thanks in advance

Disconnect the tap and see if water is flowing out of the pipe.

I have took off the flow tap no water coming through and have took off the coupler that connects to pole hose still no water coming through so I take it's the pump what can I do next thanks

You might need to prime the pump. I used to get this problem with my trolley if I ran a barrel dry.

I know it sounds bad but fill the trolly with water turn it on to max flow and try sucking the hose this will help prime it or remove an air lock , if it’s that 

If you don't have a strainer then could be more than likely resin beads could have damaged your diaphragm.