Thanks for this thread, had the same
problem with mine. Only issue was finding the darn fuse boxes. Not where SEAT say in the manual. And no numbers in the fuse box!
Mine was registering the same fault as above.
Like a muppet, I looked at the fusebox, saw the blown one and thought "There's the
problem!" and yanked it out without looking where it came from

. Trial and error, and about 4 liters of washer fluid later, I found the right location! The fuse was kind of on it's own in the middle of an empty row, which was why it was so hard to find.
You can actually hear a relay clicking behind the driver's side fusebox when the headlight washers kick in, which is useful for troubleshooting. IIRC it was location 36 in the manual, but that means nothing if the fusebox has no numbers!