Flushing central heating system question

I'm looking to flush my central heating system as some time back, i noticed sludge/almost iron fillings in my Fernox TF1 which i assume is due to lack of inhibitor

So i know i could hire a powerflusher (quite expensive) which i believe you fit in place of the TF1 temporarily, but could i achieve the same by taking a feed from my cold mains with a double check valve to prevent any back flow and contamination, and then flush the system that way with the outlet going into the drain ?

Once the outlet runs clean, i could then add the Fernox inhibitor via a top radiator and then bleed/top up as required

Does a powerflusher need the boiler running for a period of time while it does its thing ?

Is there any reason why i wouldn't want to clean the system this way or why i shouldn't ?
To me, its the equivalent of taking all the radiators into the garden and flushing them with a hose !

My boiler is a Worcester Greenstar 37cdi btw

The black sludge is iron oxide, known as magnetite, which is a result of the water in the system oxidising and breaking down the inside of rads, its then magnetised as it passes through the AC field in the pump and sticks together. Inhibitor only slows this process and does not stop it.

A powerflush machine has a powerful pump and flow rotation, so as to dislodge the sludge, with the use of heat activated chemicals.

You could remove the rads and flush individually but would struggle to remove sludge from pipework.

Thanks for the reply Crofton

Crofton Gas said:

A powerflush machine has a powerful pump and flow rotation, so as to dislodge the sludge, with the use of heat activated chemicals.

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so based on the above, i'm assuming that the central heating is running whilst the flushing happens ?

I depends how dirty it is, and if there are any perceptible problems.

You can do a DIY chemical clean quite easily with X400 or similar. Often that is enough. If not, a powerflush may be worthwhile.

It's so cheap and easy that I'd try that first.

No clean will get all the dirt out, so it's normal to get black traces in your filter, but there should not be a thick layer of sludge, and the amount trapped should decrease over time, as you capture and remove it.

JohnD said:

I depends how dirty it is, and if there are any perceptible problems.

You can do a DIY chemical clean quite easily with X400 or similar. Often that is enough. If not, a powerflush may be worthwhile.

It's so cheap and easy that I'd try that first.

No clean will get all the dirt out, so it's normal to get black traces in your filter, but there should not be a thick layer of sludge, and the amount trapped should decrease over time, as you capture and remove it.

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correction....its not so much sludge, more as mentioned before, black iron filings type appearance

i guess if the filter is picking it up, then a clean of that first and then some chemical cleaner as you say, may be all it needs

no issues noticed on rads yet in terms of cold rads etc but just dont want boiler problems in the future so want to pre-empt


thanks JohnD....will give that a try first then

after cleaning, draining and rinsing, add inhibitor to reduce future corrosion.

If you are in a hard water area you can use a limescale silencer to reduce kettling noises in the boiler. The latest ones somehow remove it without being acidic.

Sean H said:

Thanks for the reply Crofton



so based on the above, i'm assuming that the central heating is running whilst the flushing happens ?

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Yes, unless you use a powerflush machine with internal heating element. As above tho, powerflush is only required on systems with problems or new installs

Flush machine the way to go they put 90litres per min round the system so check it's ok cos there's a chance a rad may give out with the flow and leak badly when I flush the customer signs a disclaimer that exonerates me from any claim.Bob