Central heating system flush

3 Oct 2006
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United Kingdom

I've just found out that I need to flush my central heating system, it was recently comissioned and acid flux was used on some of the copper pipework..

It currently has sentinel x100 inhibitor in it.. I plan to put sentinel X300 cleanser in to remove traces of flux etc.. then refil with X100 after fully clearing the X300 (what fun) - already have the sentinel stuff so hopefully you won't all tell me it's rubbish

My question is do I need to remove all traces of x100 before I put in x300 or can I just drain down enough of the current to pull in the x300 and have them both in together? I'd rather do this as there is underfloor heating involved and it's not so easy to drain down..


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I've just found out that I need to flush my central heating system, it was recently commissioned and acid flux was used on some of the copper pipework
Why are you having to do this work?

The person who installed the system should have flushed it with the correct chemical to get rid of the flux etc before it was commissioned.

Get them back.
Curious, HOW did you find out?

What does it say on the benchmark about the flushing?
sorry, I should have explained further - am one of those pesky DIYers who has persuaded a friendly plumber to do the bits I can't (is a vented system). I jumped the gun with inhibitor while filling with water to test the primary soldering and have been told I need to put in cleanser and flush properly before it is good to go. (should have called him and asked first)

Just heard from Sentinel (wasn't expecting such a quick reply to my email) and they say the two can be mixed and will work fine together for the cleanse.. I then obviously need to drain, flush and re-fill with inhibitor added again.. which is fun with the underfloor heating loops - the UFH manufacturer just says to drain the system from the return on the manifold while continuously filling the feed and expansion to ensure a complete change of water in the underfloor pipes.. I can only assume you estimate the time it will take to pass through one 'change of water' and double it.. then do the same for the second manifold.. wot fun.


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No point doing a cold flush now so after adding x300 get system up tofull temp before draining
Add a small piece of blue toilet block to the header tank and allow it to dissolve before you start, That way when the water starts to run clear you will know that you have flushed the whole system through.
Does that really work? I thought they disolved mostly clear.. no issues with the bleach?
The blocks will dye the water blue or green, the bleach will be so highly diluted it will not do any harm, just make sure you get rid of all the dyed water incase you have a spill or a leak later on.

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