Fruitless Radiator Flushing

Had two downstairs double radiators, one large, one small, which were only heating at the top, so we removed them and flushed them outside with the garden hose. Both yielded a lot of black material. We refitted them both but after all our hard work only the smaller one heated up SLIGHTLY better - any suggestions?

Another flush in the garden, but tap the rad in the middle with a rubber hammer or the handle. to loosen the sludge.

Not with a sledge hammer or you will damage it.

Thanks for your reply DIA

I actually did tap the rads the length of each rib with a soft hammer while flushing them. I wonder if I were to remove them again but fill each with a solution of some proprietary flushing chemical, leave
them for a day or two and repeat the process, would it work better?

To tell you the truth, a other rads in the system exhibit the same symptoms, so I was considering flushing the whole system. How would I go about introducing flushing chemical into a closed system???

Normally inject it through a rad vent but you need a circulation for it to work.

Since you managed to get two downstairs rads off without disaster you appear to have managed to turn off the rad valves satisfactorily. Why not try attaching a hose to the ends of the valves and flushing the pipework also. This would clear a lot more gunge and confirm your initial diagnosis of a sludged system. If this is the case, let the hose run until clear(ish) before adding flushing chemicals, so they will have much less work to do.
Also dismantle your pump and clean out its impellor, then fit a boiler buddy (from Fernox) to show when the system is finally clean.

Go with MM with the hose.

No point just poking a hose through a radiator in the garden though, the water will just take the easiest path and you'll not clear anything much.

If you 1/3rd to 1/2 fill the rad with the hose, then with 2 people(or bungs) invert it 10 times you'll get the water running up and down the vertical channels. Flush and repeat until no more black comes, even if you bang it with a rubber mallet. I usually just use the heel of my hand cos my arm is a lot heavier than any mallet...

Yes if you left it "soaking" in a solution of say citric acid or one of the other desludgers it might help.
If the rads are awful though consider replacing them - look better and not over £££.
Replacing the rads yourself is probably cheaper than paying someone to do a powerflush!

Its very common for people to go to all the bother of removing rads etc but to forget to check that there is a flow from each rad valve into a bucket.

This checks that the pipes and valve are not obstructed and takes about five minutes per valve ( to allow for emptying the bucket! )

Tony