Rust from new boiler

[u/theoretic_theory]

A few weeks ago, I installed a new heat pump boiler, from the brand Midea, to replace our old electric boiler. According to the installation manual, the tank itself is made of enameled steel.

Since all the old pipes in our house are copper, I placed a dielectric coupling on both the inlet and the outlet. On the inlet side there is also about 1 meter of Alpex between the copper and the boiler.
Yet I now notice that the hot water is very slightly brown, and rust has collected in a collector that is currently not in use. I read somewhere that there should actually be no copper upstream of the boiler, but this advice seemed more the exception than the rule. I also know of several systems where this is the case and they don’t have rust.

So, is it true that copper pipes upstream of the boiler, even with 1 m of Alpex and a dielectric coupling, can cause rust so quickly?

[u/arizona-lad]

Flush the system. Add a rust inhibitor when refilling.

[u/theoretic_theory → u/arizona-lad]

It's for domestic hot water so a rust inhibitor won't work. But seems like general consensus is to flush so I will try that.