Discoloration of heating water (only the supply line)

Have the expansion vessel installed in stainless steel and fill with demineralized water.

I guess then it’s not just the expansion vessel but also the Kagg Mini buffer that the manufacturers like to insist on...

Do you have pictures of the rest of the system?

Nothing really meaningful since everything is integrated into the indoor unit of the heat pump.

I definitely know that a heating expansion tank as well as a small mini buffer storage with just under 20 liters are installed inside. Although I didn’t want the buffer, the installer couldn’t be persuaded otherwise because the manufacturer requires it due to minimum flow rates, etc.

They would have built the system without the buffer, but only if I had waived my warranty claims.

The simplest rule for low-temperature heating systems: as little (preferably no) non-precious metals in the system and [VE-Wasser] as possible. This largely avoids such problems.

What would you recommend there?

exactly that:

Have the MAG installed in stainless steel and fill it with VE water.

Maybe a dumb question, but with what argument can I best push through the V2A expansion vessel (I didn’t even know they exist in V2A) with the heating engineer? I assume he will suggest flushing the heating circuits as defect remediation and then refilling the system properly and correctly? And in a year the fluid will be contaminated again because the cause (MAG) is still inside? And in return, I will be sold the annual flushing and refilling as additional maintenance effort? And that will go on until he has survived the 2-year warranty?