popping & crackling noise (scale buildup?)

Does anyone in northern/central NJ know how to remove scale buildup from the bottom of a residential steam boiler (gas - mfg. Crown, model BSI103)? The crackling noise at startup was never there before. It's 4 years old and might be saved if the right chemical can break up the sediment at the bottom. It has no leaks so I doubt it's rust (yet). I think it's hard water's mineral deposits laying on the bottom. Anybody know someone good at this in NJ? Thanks!