F18 indicates a draining problem.
If it's not draining at all, check the drain hose where it connects to the house drains.
If it's onto a connection, take the hose off and check the hose and the connection for a blockage.
If ok, you'll need to manually remove the water from the machine.
(If your machine has a draining tube, use that to empty it).
Put a shallow dish in front of the filter/pump cover. (Bottom front of the machine)
Slacken the cap a little to drain the water.
Tighten the cap to stop the water when you need to empty the container.
Once the machine is empty of water, take the cap off.
Clean out any debris in there.
Look into the pump housing and you'll see the pump impellor.
Ensure this can turn and isn't jammed by a small piece of debris.
Turn it manually, there should be some resistance and it then "jumps" round.
It shouldn't spin freely.
Remove any laundry.
Put the machine on spin only.
Look into the open pump housing to see if the pump impellor is spinning.
If all ok, refit the cap and try the machine again.
Hope this helps
Let me know how it goes or if you need more help