ᐅ Black flow tubes in underfloor heating?

Good morning, we took over our house from the general contractor in November 2021. Now, all the flow tubes of the underfloor heating system are black.

Is this normal?
Should we possibly file a defect report with our general contractor or have the plumbing revised?

Many thanks for your help.

Yes, go ahead. They might say it doesn’t matter, but maybe you’ll be lucky.

A sludge separator is needed, and it must actually be used. The system should be flushed and filled with demineralized water (not tap water).

Thank you, is there any information anywhere stating that it does matter? The complaint has been submitted. Let’s see what comes next.