F15 relates to the heater in the dryer part of your appliance. This is possibly the element, the control circuits or the computer board itself. There is no way to be absolutely sure without test equipment; if you are unable to do this safely yourself please have a look in the Directories section, and see if there is a UKW engineer in your area; failing that pop your postcode up and soeone will pick up on it.
Do nothing yourself without pulling the plug first.
Regards,
Penguin45.