Think I should run some cleaner through my CH system having seen the amount of sludge that was in a [very very old] rad I removed yesterday (and it’s never been done in the 19 years I’ve been here)!!
The system was drained a couple of times 3 years ago as part of some works we were doing and there’s a number of new rads waiting to go on but about 8 rads will be > 20 years old.

I can easily drain the system down a bit and add the cleaner and let it work for a couple of weeks before the pro’s come and do some work that will involve draining the system again – so now seems to be a good time.
I’m thinking of Sentinel X400 as it seems pretty high profile – any others to consider or are they snake-oil?

For no particular reason I’ve always used Fernox. If it’s as bad as your radiator suggests I’d open all the valves – note lockshield positions before disturbing them – and run water through for a while first to get the worst of it out before I put any chemicals in.

Do you have a magnetic filter on the system? If so I’d maybe try closing all the radiators then opening one at a time and running the CH for an hour or two, then cleaning the filter. Close that radiator then move onto the next. Basically a DIY Magnacleanse treatment. When that’s done and you’ve got the worst of the crud out, then try the Sentinel cleaner.

If you havent got one I’d recommend getting a magnetic filter fitted when the plumbers come (unless your happy to do it yourself obvs). Our system is mix and match with most pretty old rads. I changed one a while ago and couldn’t believe the crap that came out of it!

Fitted a filter to the return leg to the boiler and have done various combinations of what @theflyingox said above. The system runs far more effectively now, no cold spots in the rads and the whole lot heats up quicker. I’ve added Sentinel products since, cleaner to break down remaining deposits and inhibitor to run around the system.

Just be prepared to find leaks in the pipework, cleaning crusty rads also cleans crusty pipes! Guess how I know this…

PS: if you are flushing out the system, give the radiators a tap with a rubber mallet to loosen any deposits in them.

I’ll tell you in three weeks. I’ve got X400 cleaner in my system now after installing an Adey Magnaclean filter in the return. Instructions say it can be left in for between 3 and 4 weeks. I checked the filter after a week & there was next to nothing in it. It’s a fairly big system, 36kw boiler, thermal store & two pumps. I was expecting more gunge in the filter but I’ve kept the system full of inhibitor so it looks like it has been doing its job.

Just popped a magnaclean in my system that ive been meaning to fit for about 4 years. Impressive the amount of crap its pulled out after a day!

Well I’ve just done a partial drain down and put 1L of X400 in the FE tank to do its thing for a couple of weeks.
When the system is drained down again on the 9th I’ll be looking to see what the water is like as what came out this morning didn’t seem that bad – but I know there’s sludge in there so I’m hoping for some proper black crap to be coming out.

@theflyingox, are you my plumber? That’s exactly what he told me to do, it has perked up several heating systems I’ve had the pleasure of nursing on the cheap.

From all the recommendations I’ve picked up a large Magnaclean from eBay for £45 that I’ll get fitted when the pro’s come round in 10 days.

Not only should it pick up a load of sludge over time, but it will also make it much easier to add further cleaning/inhibitor chemicals.

Over the last week I’ve learnt a lot about our CH system, including how to get rid of the air lock that has defeated others!
And what I previously would have left to the pro’s (i.e. draining down and refilling) I’m now happy to do myself – ultimately this is going to mean a cleaner, happier and hopefully more efficient system.