I'm assuming your warranty is up?
Buy a new one.
I had a very good quality, expensive iron several years ago, it did the same thing. My son loves to take things apart and fix them, so I handed it to him. He found that the thermal fuse had gone bad. Ordered a new one, installed it, iron worked great.
Problem is, it took him quite a while to get the iron taken apart and put back together. If I'd paid some technician to fix it, it would have cost the same as a brand new iron.