Which is the most effective C/H Sludge remover?

[VxDuncan]

While we're having an evening of CH questions...

I have two (was one ) rads in my house which simple don't get warm. Before I have to go down the powerflush route I'd like to try a session of sludge remover first. I've flushed it a couple of times without much luck, once with a cheap (screwfix no-nonsense system cleaner). Which is the most effective sludge removal chemical? Possible something like the sentinel X800?

Bit of back ground:
1930's semi. Was open system, converted I guess 10-15 years ago to closed. Didn't have any method of draining the system at all - I had to fit a drain valve where I could, which is now almost blocked... Guessing it has 40 years of crap. Been drained / refilled a few times recently, but still no good. Have found a couple of radiator tails totally solid with sludge. The radiator I most want working was okay till recently. is full of water, which passes through the fill side (with a trv) okay, but the lockshield on the other side must not be allowing any flow. Other possibility is a massive airlock as I've found a random hot pipe in the loft in the past, so know they is some CH plumbing up there. I've tried closing off all the rads apart from one to divert max flow and clear this rad with no luck.

Any ideas welcomed )

[Ricky_M]

X800 is meant for powerflushing, possibly too strong to be left circulating. X400 is more suitable to your requirements, it works very well over the course of a few weeks.

[douglasr]

The scottish gas engineer that visited me recently did a similar thing to you (switching the other radiators off). In the end he removed the radiator, took it outside and washed it through with a hose (a power washer would be better). Worked a treat, although it took about 20 minutes of lifting shaking and flushing for it to run clear.