Turn off the filter and unplug it from its outlet.
Remove the flow sensor and the adapter. Look in at the electrolytic cell inside of the filter. If it has scale on it you need to clean it off.
Place the high-powered nozzle on the hose and turn it on. Spray the electrolytic cell with the hose to remove any debris or scale.
Replace the flow sensor and adapter, plug the filter back in and turn it on.