Yup.

As an engineer, perhaps the most important part of my job is to put my foot in it. Toxic positivity is deadly.

You have a situation that is, in theory, impossible. Yet it is happening. Cheer up, that's how discoveries are made! Thus you have two options. a) Do nothing. b) Get data and figure it out, get some closure for the issue that haunts you, you'll feel better about it, guaranteed lol

Bullshit.

Rubber hoses do let in some oxygen, but that oxygen will travel in the circuit to corrode iron somewhere else. Just because some O2 enters in the hose doesn't mean it will "attract" sludge or particles into the hoses.

When I took out the 40 year old rubber hoses from my installation, they were absolutely okay. I mean, the rubber had gotten a little bit stiffer than new, and the inside was painted by brown sludge, but there wasn't a single particle in there. All the corrosion flakes were at places where flow slows down so they can settle (bottom of the buffer tank, radiators, etc) and of course in the heat pump exchanger since this has small cross section and acts as a filter.

FYI I drew a sample from my heating water

This is the kind of particles you'd expect from cast iron or steel corroded by oxygen. Scale in cm and mm. Unfortunately the cell phone camera can't tell the difference between rust (brown flakes) and magnetite (black particles) but it is clearly visible.

Completely different from yours. I bet it's not corrosion and this stuff was probably already inside when you got the equipment.

They're not rusty, so not steel. You can always try with a magnet.

Crush it with some pliers to check if it's rock / mineral or metal.

Heat it with a blowtorch:

- Melts : aluminium

- Burns while melting: thermoplastic

- Burns while not melting: most likely rubber

- Does not melt: stainless steel

Honestly this looks like someone in the factory dumped a bin of metal shavings or other detritus into a pipe and you got the equipment delivered with the crap inside.

Are these shavings present on:

- Both sides of the heat pump?

- Only one side, which one?

We were told by experts, including at Vaillant, which we consulted on multiple occasions and who were very reluctant to respond to our questions, that most of the corrosion accumulates in the rubber hoses inside the heat pump because the hoses do not have an oxygen barrier and are a common place for the accumulation of corrosion. The buffer cylinder may be corroded/damaged by corrosion on the hot water side. The condenser may be damaged / full of corroded particles

We were told that, “If the condenser fills with corroded particles, then it would potentially affect efficiency due to poorer heat transfer, this could cause issues with the operation, this will only become known once the heat pump started faulting, flushing may help in some very rare cases but generally does not solve the problem, systems are always recommended to be flushed and chemically treated upon install, a suitable filter is also recommended." While, over a two-year period, we found various people within the GSHP industry who were willing to discuss these issues after a lot of repeated correspondence, what we were unable to do was find an expert witness who would testify that:

• The brine side of the heat pump may be damaged 
• The efficiency of the system may be compromised (COP)
• The life expectancy of the system may be compromised (20 years+)

Further, we thoroughly investigated the training and guidance provided by the GSHPA and the MCS at the time, and there was no reference anywhere to corrosion prevention, nor were certified installers required to have certification or training in basic heating and plumbing which, of course, covers corrosion prevention as an ABC. This may no longer be the case as we drew a lot of attention to this problem when we were investigating the causes and consequences of corrosion in heat pumps and attempting to take action against the maintenance company. At the end of the day, the maintenance company was trained according to standards of the day and was probably largely unaware of both corrosion and the means to prevent it. They are certainly aware now. 

I'm baffled at the size of these metal flakes, they're huge! This doesn't look like the usual sludge from oxidized iron at all! What the hell happened? Where does this stuff even come from? What kind of metal is ut? You have a lot of aluminium radiators?