Hotpoint F05 error and warranty?

If I remove the cover from the filter to see if it's got something in it, will that invalidate the warranty? By way of background the machine stopped working altogether after just four washes and the Hotpoint engineer came out this afternoon to replace someting on the computer panel and now it's working again, but when I get to the spin bit it won't go any further and flashes up the F05 error code. I think it's more likely to be another fault with the computer because when I ask it to run the spin cycle alone, it does. And it will drain. But I don't fancy getting the engineer out again because it's such a pain when you work. If I can try this first without invalidating the warranty then I will