Flushing a closed central heating system

I've got a closed central heating system with a combi boiler. I added some fernox restorer last week and would like to make sure it is all flushed out.
There are two valves which I used to drain the system down with - but gravity doesn't always do its job fully when draining it down by opening the valves on their own.
I thought that if I open both of the draining valves, and then opened up the tap which I use to top up the closed system with water, would that effectively flush out the whole closed system.
Am I being naiive? :-)
If not, what would you all suggest as the best method of fully draining the system?
Thanks,
Aris
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aris wrote:

This method can work very well if the mains is up to the job. Make sure the water goes the long way round through the rads (open just one at a time) and not the short cut straight to the drain!
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Ed Sirett - Property maintainer and registered gas fitter.
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