@aventus-eco any words of wisdom here?

Very similar to end of life heat pumps that can't get scrapped until refrigerant is recovered.

On the wider point... you're right to be annoyed. Glycol in residential heat pump systems is often specified as a default when it isn't actually necessary. If the system is designed correctly with adequate freeze protection through flow management and controls, many installations simply don't need it. 

I'll make some enquiries tomorrow with my installer network.

https://www.cityoflondon.gov.uk/services/waste-and-recycling/hazardous-waste-collection

Can't get anyone to take it - even the council. Those responsible for the environment really need to ensure a path for this.

Which level of council did you speak to?

District and Borough Councils have responsibility for Environmental Health and domestic refuse collection.

Country Councils and Unitary Authorities also have Environment Health, together with recycling centres, trading standards etc. They also appoint representatives to other statutory authorities such as the regional Rivers Authority, Water Supplier and the Environment Agency.

If 'the council' aren't providing you with guidance, then this should be taken up with the Councillors for your ward. Elected Members run the Council, even if they've appointed an Executive Board. Councillors can instruct their officers and hold them to account.

Posted by: @seoras

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How to dispose of 100 litres of glycol mixture?

Propylene glycol: safe, often used as food additive, you can probably flush it, unless contaminated with other stuff.

I've spoken to installers about this before, and it's not quite that simple, unfortunately. Even propylene glycol (yes, technically food-safe in its pure form) becomes a different proposition once it's been sitting in a heating system. By that point it's carrying corrosion inhibitors, metal particulates, flux residues and whatever else the system has shed over the years. That cocktail absolutely should not go down the drain.

There's also a wider environmental point worth making. When glycol reaches waterways in any significant quantity, the bacterial breakdown process consumes so much dissolved oxygen from the surrounding water that it can effectively suffocate aquatic life, and notably, propylene glycol actually persists longer in the environment than ethylene glycol and consumes more oxygen while breaking down. So the "it's food-safe" argument doesn't hold up once you're talking about waterways.

The correct route is to treat it as trade waste. A local waste disposal contractor or waste facility will take it... some plumbing merchants also offer disposal services. It's worth ringing around.

Whatever you do, don't pour it on the ground either... glycol is toxic to animals even in relatively small quantities.

Particles floating in the water are a problem with moving seals like air vents or pressure relief valves, they get stuck in between the rubber seal and the surface it's supposed to seal against and then you get a leak.

Photo of the water and bits please, with ruler or tape measure for scale. Are they attracted by a magnet?

> I can't think where the rust comes in

What parts of your installation are steel? Radiators?

How to dispose of 100 litres of glycol mixture?

Propylene glycol: safe, often used as food additive, you can probably flush it, unless contaminated with other stuff.

Ethylene glycol: toxic, treat as hazardous waste.