On Wednesday, 20 November 2019 07:57:15 UTC, Andy Bennet wrote:
As I am getting on in years and no longer fancy climbing ladders to
clean the upstairs windows, a while ago I bought one of those water fed
pole brushes and a pressurized water deionizer to do the job. I must say
that it does an absolutly brilliant job in next to no time and wished I
had invested in such a kit years ago. I use it for the downstairs
windows as well as it is so easy and fast.
But I digress...
I need to do a small amount of system pipework relocation on our
(sealed) CH system next year and the thought crossed my mind, as we live
in a very hard water area, that I could repressurize the system with
deionised water and inhibitor.
This would help to prevent scaling up and kettling noises in the boiler.
Now I know that pure water can be quite agressive in terms of corrosion
etc etc but is this a good idea or should I just forget it and top up as
normal?

Limescale is not a problem in CH systems as there is only a small quantity of water involved, ie the same water recirculates.
The crap you may find in your boiler/radiators is the result of corrosion (sorted out by an inhibitor/additive to the water).
There are different inhibitors for different metals in your system (eg you may have an aluminium boiler),

The other cause of "kettling" is poor water flow due to bad design of the CH system/pipework.