Black water when bleeding radiator

[timber]

I had a new radiator fitted in April and my plumber said he added inhibitor.
When I bled a radiator recently the water was black, is this normal or should the water be running a clear colour?
If I have to flush the system is it best to run through a cleaner first and then add the inhibitor, as there are a few products on the market what brand is recommended that I use.

 

[JohnD]

the black is probably old sediment. making changes to the system tends to disturb it so it is carried around in the water. sediment is undesirable as it can clog the pump and boiler and may cause blockages.

if you decide to drain it, run Sentinel X400 in the radiators for a month first. It will cost you £15 for a litre and will loosen old sediment. It is a mild cleaner and non-acidic.

you never get all the old dirt out, so if you can afford an extra £100 for a Magnaclean and fit it yourself while drained (a fairly straightforward DIY plumbing job) it will continue trapping circulating black sediment indefinitely.

If you wait until you have a blockage it will cause a lot of trouble and be a LOT more work to clear.

after cleaning, add inhibitor such as Sentinel X100 again on the final fill.

two good brands of chemicals are Sentinel and Fernox.

see also //www.diynot.com/forums/viewtopic.php?t=37170

 

[timber]

Thanks John for the reply, first job for the New Year!