F1 error usually signals a problem with the control board. However, there are a few other things you can try before spending money on a new control board
To remove the error, press Pause/Cancel twice. Unplug the machine for 2 minutes and then plug it in. Select a cycle and press Start. In some cases, this will reset the F1 error.
If your machine is under warranty, you should of course contact Whirlpool and they should repair it free of charge. Even if it's out of warranty, note there seem to be a lot of people who experienced F1 errors on Whirlpool washers and there has been a recall of some models. You can contact Whirlpool and see if your model is one of them.
If this doesn't work out, here is what you can do. The reason for the error can be blockage inside the pressure switch hose. You should check the hose for blockage and there are instructions online on how to do it. If the hose is fine, you should then most probably replace the control board. It's an easy repair. Here are the instructions on how to check the hose and how to replace the control board: Whirlpool F1 Error
Hope this helps. Let me know if you have any other questions