Flushing out a central heating system.

Postby Jhdj13 » Thu Oct 16, 2008 4:55 pm

I'm planning to install a new combi boiler, but I'm advised that flushing the system first is necessary. Howevever, in the interests of economy, I'd like to avoid the cost of getting it back-flushed. I've no problem draining the central heating system down and re-filling, but will that do the trick?

Any advice for a DIY'er?
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Simply Build It

Postby Steve the gas » Fri Oct 17, 2008 4:16 am


Power flushing would be best but, you can drain & refill a few times until no sludge remains (some will remain) then push mains water thru the rads at suitable points.

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Postby chris_on_tour2002 » Sat Oct 18, 2008 9:52 am

check the manufacturer's guarantee carefully - some state that a power flush is necessary. if you don't do it you might absolve them of responsibility if any manufacurer's faults develop with your boiler during the guarantee period.
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Postby AdamsHeating » Sat Oct 18, 2008 9:53 am

hi there, if your current boiler is running fine, just chuck some sentinel X400 into a radiator. I know a council that do this and they rarely have trouble due to blockages and they never powerflush...

this is what the website says so follow the instructions:

"1 litre of Sentinel X400 is sufficient to treat a typical domestic system of 8 to 10 radiator panels. Larger systems should be dosed with 2 litres. To clean an existing system in accordance with BS7593: Sentinel X400 should be circulated, preferably at normal operating temperature, with all valves open and the pump turned to a maximum flow for a minimum period of 2 hours or until satisfactory performance is restored. Where systems are badly fouled, a longer period of circulation (e.g., up to 4 weeks) is recommended, but the product will not clear a completely blocked pipe"

That should clean up your system enough for a new boiler to be installed.

For the record, I powerflush, but this is a far cheaper way of clearing.


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