Bolier Water Quality

Jeff_44

I have all the signs of dirty water in my steam boiler:
slow to heat, bouncing in the sight glass, and when
I boil some of the water on the stove, it foams. The
trouble is, the boiler is old (60 years or so) and I've
looked on the manufacture's web-site (weil mcclain)
and can find nothing that discusses the cleaning of this
particular boiler (series 2, size 6831).

I realize I need to have a pro do this, but 1) I cannot
find a reliable pro in my area (Rochester, NY)
and 2) when I do, I want to be as educated as possible.

Any help would be appreciated.