Backflush Of Portable V2 Control unit 

Cap the ports on the inside of the spa. It will either be 2 or 3 to screw on, make sure the gaskets are on the inside of these also. 
 
Turn the power off from the socket or unplug the control unit.
 
Remove the filter from the housing and the filter grid. Then use a garden hose through the heater port to backflush the control unit. 
Continue to flush out the dirt and debris, water will exit from the the filtration port so it's clear of water as much as possibe.
After several minutes, drain out as much hose water as possible from the control unit. 
Make sure the filter housing is as dry as possible.
After this connect the unit back to the spa, purge the unit and engage heat once again.
Backflush of control unit video

Article published by Ali Green