Viessmann boiler failure

[ppppenguin]

Back to my boiler. I've just added another litre of Sentinel X100. When I let off the pressure (via the Magnabooster) I got a few fragments of black iron oxide. So either the system has been making some or there were some hidden residues that the DS40 failed to clear out. There was also a bit of a surprise. the first bit of water was a dirty grey colour with the fragments of black magnetite, I sort of expected this. Then it ran clear, then it went reddish brown, like rusty water though the colour may not have been quite right. To get red iron oxide you need oxygen in the system, something that I really doubt is present in a pressurised system. If it really is red iron oxide (haematite) then radiators can rust through very quickly indeed. Then it ran clear again, then a bit more reddish brown, then clear.