Sulfuric acid can be corrosive to metals, though it depends on the type of metal, the concentration of the acid, temperature, and how long they are in contact with each other.
Any idea what the heat exchanger is made of? You might want to do a spot check in an inconspicuous/inconsequential spot before soaking the whole thing.
What needs to be cleaned off? I assume some kind of hard water deposits. Is it mostly calcium carbonate, calcium sulfate, or a mix of both?
Any idea what the heat exchanger is made of?
I might guess the exterior is stainless steel but I’m not a chemist. Magnets do not stick to it.
What needs to be cleaned off?
The previous one (removed in 2019) is clearly ram-packed with the kind of yellowish-white limescale flakes which resemble what builds up inside water kettles.
I typically clean water kettles using white distilled vinegar to lift the flakes and pour them out. But I suspect that might not do well in the heat exchanger because the flakes seem to be packed in there. To clean a hot water dispenser (which is for tea but very similar to a coffee maker), I use a proprietary descaling solution which seems to actually dissolve the scaling. No flakes are expelled in that process. So I am tempted to use that stuff, but I don’t really know if the coffee machine cleaner reacts with stainless steel or if stainless steel is what i am dealing with.
I’m guessing the currently installed heat exchanger might be clogged with something different. I think after just a few years the tap water side of it would not be clogged yet. But in the summer I flushed a few radiators and ran radiator cleaner through the system. Drained that out, refilled, then added “inhibitor” which prevents corrosion in the radiators. I lost hot tap water service after increasing the pressure in the radiator circuit. So I wonder if the cleaning solution caused debris to circulate and get trapped in the exchanger. There might be a mixed bag of sludge clogging the current heat exchanger.