mtfallsmikey,
Sodium Hydroxide is indeed common lye. It is also the main ingredient in many drain cleaners.
That said, be very careful to get PURE lye. Many drain cleaner products contain other ingredients besides lye that you probably don't want in your boiler. Pure lye is getting harder to get because it is used in the production of methamphetamine.
Lye is super caustic. Keep it off your skin and wear eye protection when handling it. It also produces a lot of heat when dissolved in water... enough to crack glass containers and melt plastic ones. Always add it slowly to cold water.
Last, but not least, a little goes a long way! If you don't have guidelines on how much to add, start with a very small amount, allow it to circulate through the system for a day or so and re-check the pH.
Hope this helps!
Adam