Will it work? What are the dangers?
 

Hi, I ended up not doing it, but I had a two litre bottle of water with added Calgon. I'm pretty sure I read on here that it would make the matrix sparkle :D

#Heater matrixes last longer with calgon!

Catchy tune! :D

Descaling cooling systems can often end with a leak, the lime scale and debris that builds up over the years will clog up fine waterways but it also seals up small leaks.

My advice when ever you top up a cooling system is to use distilled water rather that tap water, it is not expensive and saves a lot of contaminants entering the system. Look at your kettle and that is what parts of the cooling system will look like if you use tap water.

Doesn't the amount of limedcale build up and stuff in kettles and washing machines vary depend on where you live as you get hard and soft water?

This is misleading. Solids in the water is typically less than 1g per liter. The kettle sees a fresh inflow of perhaps 1000 liters a year, the cooling system after a couple of refills maybe 25.
The sediment in the kettle happens mainly at the heating element, where water boils off. A similar localised boiling does not happen in an engine, so most of the solids stay in suspension.

You can thus safely use tap water for your cooling system.

As for cleaning the matrix in situ. flush with a garden hose through the heater hoses, and change direction of flow from time to time. If you have access to compressed air, you can fill the matrix with water and give a blast of compressed air, to blow the content out under pressure. Do so with moderation, depending on the pressure. If you empty the outflow in a white bucket, you can see the results, I guess you will be fine without any descaler.

Let us know how you get on.

It is quite easy to take it out flush it then test it with boiling water

Left descaler in mine for a couple of days, no harm done but tons of crud came out, flushed it thoroughly, used descaler again and got more crud, so it doesn't hurt to use descaler, eventually no crud and a very hot matrix at both ends.

Many people have found it very difficult to get it back though. I have never tried, and I see no reason to try, unless you want to replace it.