How do identify rusting radiators causing sludge

[u587162]

I have 14 radiators, most of them installed between 12 and 20 years ago. One old one from the 1970s.

I keep getting sludge build up blocking my Viessman boiler heat exchanger and done a powerflush 2 years ago and the water is getting murky again. Cleaned out the Magnaclean a couple of times in the last few days and there were a few flakes stuck to the magnet. If I do have a rusting radiator, how do I diagnose this as I cant afford / dont want to replace all of them.

 

[Jurassicspark]

Is there any inhibitor installed in the heating system?

If not then your radiators will rust their souls away.

 

[JohnD]

Have you got a feed and expansion tank in the loft?

Or does your boiler have a pressure gauge?

 

[u587162]

yes for a while we did before emptying the system before replacing a radiator and forgetting to put some back in. Does it really make a difference?

We have a combi boiler with a built on 40 litre tank - Viessmann. So yes a pressure gauge

 

[Justin Passing]

Yes it makes a difference but not as much as with open systems. Those which never had any flushing or cleaner/ anti-rust type additive would have all the flux residues too. Some combi systems stay clean forever.
The 40 llitres in your combi is presumably tap water not "boiler" water?

In your case you can flush each rad one at a time thrn the boiler with mains water (in situ), add inhibitor and hope it all is better thereaffter, but I did that and still had to clean the secondary heat exchanger every couple of years. So then you start wondering about micro leaks but they should be less likely on a pressurised system, etc etc... "Sludging" systems seem to stay "sludging" but I haven't carried out any scientfic analysis!. If you add inhibitor ro a rusty system, all the rusty particles will get protected... So use a cleaner like X400 for a month, flush, then add X100.

 

[Jurassicspark]

yes for a while we did before emptying the system before replacing a radiator and forgetting to put some back in. Does it really make a difference?

It does. To check if you have a reasonable amount of inhibitor in your system will be to:

Drain out a half cup of water from the heating system and put a nail in the water. After a few hours inspect the nail if it has rusted then you'll need to re top up the inhibitor. Not a very accurate test but it does prove a bit.

 

[JohnD]

If you use X400, it will loosen sludge, and the Magnaclean will catch whatever circulates. You will see it collecting on the magnet.

You should still drain it after a few weeks and add X100 in the final fill.