NF stands for ‘no flow’, i. e. your washer is not getting enough water. This may be due to low pressure in the system or a problem in the inlet hose or valves.
Check the pressure. To do so, disconnect the hose from the unit, put it’s end in the bath or bucket and briefly turn the tap on. If the water is running ok, you need to check the inlet valve.
Particularly, you need to check its screens for debris and buildups. Disassemble the valves and remove the screens. Remove debris, if any. If there is too much mineral buildup on the screen and the valve’s components, replace the valve and the screen. First, remove the top by undoing the three screws on the top panel’s back. Pull the top back and off. Remove the valve’s wire harness. Undo the screw, which holds the valve to the machine’s body. Now you can start checking the valve.
Finally, the error may have occurred due to a kink or clog in the inlet hose. It is not recommended to use steel-brraided hoses with thiss type of washer, because they tend to fail without any visible reason. Please, use conventional hoses instead. If the hoses are all right and there is nothing to affect water flow, there may be a problem in the electronic inlet valve. It simply, won’t let water in. Please, check the valve and, if necessary, repair/replace it.