Sony Xperia 5II

[RichardC54]

My Xperia 5II has developed a fault whereby thin dark lines appear on screen which then get broader and broader until the screen is almost totally obscured.

I tried doing a factory reset that seemed to cure the problem temporarily but it soon returned. Doe this sound like a hardware or software problem?

[BandOfBrothers]

Sounds like a hardware issue @RichardC54 

[AnnS]

Follow the repairs process @RichardC54 and book your phone for repair here: How do I book a device in for repair? 

edited to add:  Vodafone offer a 24 month warranty on the device from the date of purchase here: warranty if the phone is still under warranty you can expect a free of charge repair.

[BandOfBrothers]

in my experience @RichardC54 the manufacturer knows their hardware better and software better than a networks repair house so it might be also an idea to.contact Sony to ask if they could help.

Unfortunately if the phone shows any signs of damage aesthetically or the water sensors have been tripped then they or Vodafone could levy a fee for repair.