I was in a similar boat with my last job doing Support/QA/Custom Development for 2 years while the "official" devs went off and made a new version of the product. About a year and a half in i brought it up and they agreed to move me out of support, but the pay raise wasn't nearly adequate for the duties expected. And I regretfully agreed to half raise now, half a raise later... (24k to 32k total) and ended up getting dev/support removed leaving me with QA (devs wanted dev back and I wasn't invited to the party). I promptly left the company and found a much better job doing Dev for 55k, which sadly burnt some bridges with people i liked.

They will likely agree that you should be moved more officially into a dev position, but since you're moving up within the same company you shouldn't expect to get paid what you think is adequate for the duties. Giant pay bumps are an extreme rarity when moving up in the same company. This isn't just an IT problem, but it is why developers don't generally stay at the same company for more than 2-3 years.

Have a friendly conversation with the right people about it, but make sure you have terms laid out that you can agree to in the long run with them, otherwise start looking elsewhere.