Just wondering best way to go about doing a coolant flush, i get the jist of it, but nothing in detail about the 2007 vectra
is it as simple as it seems?
drain radiator at bottom when emptied, re-tighten the valve/seal then fill up from expansion tank (leaving the cap off?), then run the engine with heater on and fill up tank when needed til it doesn't lower anymore?

what am i missing (if anything)

 

Thanks ahead of time!

You are correct in most of the procedure but I would put the cap on before the temperature rises too high.
Once if has had chance to settle down then release the cap when safe to do so (gradually to allow pressure to release and keep clear of the boiling water).
The level will then drop slightly. Refill to the level and do the same until the level no longer drops.
Always ensure the cap is tight and never release when hot and with too much pressure behind it.