miamichillin99 wrote:Should I descale just the heat exchanger some more to clean whatever is causing the blue?
I would not recommend that. Suppose the blue is associated with copper in sulfate deposits - the acid would not dissolve that and you would be risking more corrosion for no reason.
What I might try instead would be to go through a long descaling procedure, but instead of descaling solution use purified water spiked with a tiny amount of protective bicarbonate buffer. About 0.3 - 0.4 gram of sodium bicarbonate (baking soda) per gallon of distilled would be good. That would dissolve sulfate as effectively as a harsh acid solution but would be harmless to the machine. Can't hurt and may help.