We have a rather old McDonnell & Miller oil-burning boiler which serves a
six-unit apartment building.
At some point in the distant past I was told that the boiler needed to be
flushed for two minutes once a week. I was told that the system should NOT
be running when I started this operation. To flush while the burner was on
might crack the boiler, I was told. Knowing nothing abut the system, I
accepted this without question.
Recently a plumber told me it was the other way around: The burner should be
ON when I do the flushing. I should start the flushing slowly until the
water became warm, then open it fully for 30 seconds or so. Then I should
Which of this advice should I follow? I can't find any help in the manual.