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"Flushing/Descaling" a Bosch Greenstar Combi 151 boiler (zwb 42-3)
My original installer sent two different techs to my home and offered an "annual routine flush/descale" of our boiler system for a lot of money. The problem is I got two different stories from the two techs that came out (at different times)
One tech said they only flush the water supply lines (circled in yellow, #1 & #5 in the diagram), but another tech said they also flush the heat supply lines (circled in red, #2 & #4 in the diagram).
Any input would be greatly appreciated. I do not want to spend many hundreds and have only half the job done, or worse, have the wrong lines flushed.
NOTE: this unit provides both hot water AND heat to the home. I think most systems have only hot water, and therefore only need that flushed. Mine has two systems, hence my question.