Discoloration of heating water (only the supply line)

We also had that in the old house, then at some point flushed the system and had new "suitable" water filled in. Pretty annoying.

With us, after one year it is really brown soup, you can't even read the viewing glasses properly anymore.

I would address it early on, because with us it only became apparent after more than 10 years when some rooms no longer regulated as usual. The valves had been damaged.

What would you recommend there?

I will criticize this with regard to the warranty during the handover of the house at the end of the week.

Request proof that the system was filled with the appropriate water according to manufacturer requirements and the VDI.

And request proof of material compatibility from me.

So beat a few drums and see what comes back.

If the heating engineer is so sure that nothing will happen, (according to the motto we have always done it this way, never had any problems) it should be no problem for him to confirm this in writing.

Have the MAG installed in stainless steel and fill with [VE-Wasser].