As we said the other day I actually have no idea! When I was at school two people used to come in every 2 weeks from the hospital to check everybody's' hearing aids. Though from what I could see it was basically cleaning moulds and making them whistle!
I went in as I thought my hearing was worse- it was, a little, but the main thing is one of my aids just isn't as clear and loud as the other, and it used to be. Have to live with it til I get the new ones. Given that I was told their aids had improved in 3 years, and told to come back for a new pair, it might be worth going at least to say you feel that you're not hearing as well as you used to (if that is the case).