Going to flush out my radiator system - is this right?

25 Apr 2006
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United Kingdom
Hi Guys,

Right, just before Christmas, i bled some of my radiators & discovered that the water was very black (i have a conventional (Traditional) Boiler System).

The last time the system was drained was in 2007 & this was done by a plumber who was taking out a radiator.

So, I just wanted to make sure I'm doing this right (i cant afford a plumber at the moment & i'm pretty sure its a simply task).

1. Shut off water & turn off the central heating system.

2. Attach a drain hose to downstairs rad - luckily i have a rad right next to my back door with a drainage valve/tap.

3. Open drain valve on rad & allow water to drain.

4. Once water has drained away open the bleeding valves on the upstairs radiators followed by the downstairs ones to allow any access water that is left to drain away.

5. Once water is drained away close all the bleeding valves & close the drain tap & remove drain hose.

6. Add Sludge Remover to the system into the radiator header tank - now this is the small one in the loft NOT the large one isnt it?? (quite important not to get this wrong! ) I've been told to use this treatment to dissolve any sludge that may have gathered in the pipes etc.

7. Turn water back on & allow system to fill up. Bleed rads to allow water to fill them up.

8. Once the system is filled up & all rads are bled turn Central heating back on.

9. After four weeks of running the central heating system, repeat the process but this time add the normal inhibitor

So, is this ok?


edit: Would X800 be better than X400 for removing gunge/deposits.
btw, the CH system it about 14 years old.
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If you have any significant problems with your system, this type of treatment is highly unlikely to make any discernable difference.

If you don't have any sludge problems, put some X100 inhibitor in there and leave well alone.
Your method will work, but here are some suggestions:

1. Clean out the small tank before you begin, so none of the sludge etc in the tank can get into the system.

2. Leave the water on (after cleaning the tank) so the water pressure helps to shift the muck in the pipes and rads. Keep the water running until it is clear.

3. Shut all rad valves except the one with the drain tap which should have both valves fully open - remove head from any TRV and count the number of turns for lockshield valves. Allow the water to go through this rad for a few minutes until clear, then close both valves and move onto the next rad.

PS Make sure you don't have more than one rad with a drain tap - I know we do.

4. When you have done all rads, shut the drain and turn the water off.

5. Open drain and let some water out until the level in the small tank is just above the outlet. Add the cleaner, e.g Sentinel X400 and turn on the water.

6. When small tank stops filling, turn of the water and open the drain.

7. When level has dropped to just above the outlet, close the drain and turn the water on.

(The purpose of 5 - 7 is to make sure the cleaner actually gets into the system)

Repeat the above when adding the inhibitor, e.g X100.

You can leave X400 in for longer than 4 weeks if you want to, it won't do any harm.

X800 is better for badly sludged systems, but you must follow the manufacturer' instructions.
What sort of warranty are you offering on that, D_H?
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I dont have any problems per-se. But i thought using the X400 would be a good idea to make sure that any build up in the pipes get dissolved & flushed away when i drain it the second time.

Thanks for that - some really useful addtional tips.

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