Usually nothing is done until they do not supply the hot water needed. Then a bunch of valves & an acid pump, pumping reverse to the normal flow of water...until it flows easily or 5 minutes, which ever comes first. It's smelly, somewhat dangerous & you have to have an acid pump. Acid used to be $19 a gallon. I bought a gallon last year & it was $45!!!!
PS While I was doing that sort of thing on a regular basis, we never burned through a coil (watch those 5 minutes) ....but it can and does happen, so there's always the possibility you immediately need a new coil.