F18 indicates a blocked filter. It can be difficult to open it and, consequently, to check the hose between the tub and the filter catch. Its cap won’t open, so it will be hard to deal with the blockage. Disconnect the machine from the mains and try to open the door. Take the wire ring off from the front of the gasket. Press the tub toward the back and, simultaneously, the gasket into the tub. Get to the pump and take off the pump clamp. Provide towels and buckets, because water will gush out of the tub and it may flood the area around the machine. Be ready to promptly soak it all up. Unblock the system and reassemble the unit. Most likely, the will be no error after that.