What does this debris look like to you?

[Sergiu Grosu]

We've recently done a power flush on a system that's already been power flushed twice within the last 5 years. System boiler with an unvented HW cylinder and 3x UFH manifolds. Quite a large house. Strainers installed before each manifold - fully clogged.

The stuff we got out of it looks like in the picture below. My guess - the green/yellow stuff is bacterial growth, but some of it feels like sand, which I can't explain.

What does that look like to you?

 

[ShaunCorbs]

Are you running biocide as you have ufh ?

 

[Sergiu Grosu]

Sorry, I didn't make myself clear - I'm not the homeowner, I'm the engineer who did the power flush. Yes, we topped the system up with MC1+ and MC10+ after the flush. We also installed an Adey Magnaclean HP (Dual-action) and recommended cleaning it twice a year in the first year, then yearly. It's clear to me that's biological contamination, but the grit/sand?