I do agree with Linn and probably should have explained a little more. If a qualified boiler water treatment company does the job they should cover all of the issues including making sure the boiler is acid free and the acid is properly disposed of. An acid wash is by no means a do it yourself job. However the acid does a good job getting down into the places the needle scaler wont. If your restoration is going to include major firebox work than that is probably not going to be an issue anyway.
Tom