Cleaning underfloor heating pipes and manifold

[Lower]

I noticed a few weeks ago that the transparent flow meters for my underfloor heating have started turning black from what i presume is bacterial growth in the underfloor heating pipework.

I suspect this may be due to me draining the above floor radiators a few times when i've moved radiators etc and refilling the system with inhibitor, but no anti bacterial additive.

What do i need to do to kill and flush this muck out of the system? Can i just dose it up with anti bacterial additive like fernox F7 and leave it (i can cope with the flow meters being a bit mucky internally) or do i need to flush and refill the underfloor pipework?

 

[CACKATALLTRADES]

I imagine it is just some magnetite sludge from your system cleanse.
That doesn't preclude there being a bacterial buildup as well, of course.

 

[Lower]

I imagine it is just some magnetite sludge from your system cleanse.
That doesn't preclude there being a bacterial buildup as well, of course.

I didn't do a specific system clean, just drained it down the pipe work a couple of times. I didn't drain down the radiators or the underfloor pipework. The sight glasses on two of the three underfloor heating loops started getting murky about 6 months after the second drain down and have gradually got worse.

I have a magnetic filter on the system too which is pretty clean.

 

[CACKATALLTRADES]

Ah I see, well you're probably right then. Can you not run the system hot periodically to sterilize it? Obviously important to check what the plastic etc will tolerate.