Draining a primatic cylinder

Just examined my hot water cylinder prior to draining the CH, and discovered it's primatic... this doesn't overly bother me because it's being replaced in a week and a half with a combi boiler, but before that I need to replace my rad valves with thermostatic ones.
Is there anything I need to be aware of when draining down the system? I realise I need to close off the rising main feed to the header tank - is there anything else? Similarly, is there anything special I need to do when refilling. I realise adding inhibitor is a bad idea... A google search only turns up someone with a horror story about draining one, but no advice...
I have a back boiler - the front is marked Baxi Bermuda G2. The sole control is a knob with 0,1,2,3, lightning symbol, cross symbol. Presumably if I turn off the power and gas supply to the boiler when draining I will need to relight the pilot light afterwards. Does anyone have a clue how I am supposed to do this (no manual anywhere, and no one to ask - the previous owner is dead...) I can take a guess that turning the knob to lightning symbol might accomplish something, but it would be nice to have a clue in advance :)
Thanks for any advice!
Ben
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It'll be the main cold water storage tank rather than a header tank (i.e. big rather than small) if you've got a primatic.
- is there anything else? Similarly, is there anything

should be OK

yup, turn to lightning symbol and you probably have to push it in to let gas through to the pilot (depending on the type of gas valve) and then push the button beside it which should create a spark to light the pilot. You'll usually have to push the spark button several times. Once the pilot lights keep holding the control valve pushed in for 30s or so an then when you let go the pilot shoudl stay alight and the main burner should fire up if you turn it to 1, 2 or 3. If you don't have a spark button you'll have to find the pilot (should be a window the size of a large postage stamp) and light it manually - not easy on a back boiler as it's usually buried away a foot or so back underneath the gas fire part of the appliance.
If you have a gas blowlamp and some thin pipe (e.g. gas fire or brake pipe) you can tape the pipe to the nozzle of your blowlamp (covering any aeration holes at the base of the burner) and light the gas coming out of the other end of the pipe and use it as a taper to reach the pilot light hole.
However if you turn the boiler control down to 0 so it doesn't fire up the main burner you should be able to drain the system enough to replace your rad valves without switching off the gas to the boiler - the boiler should stay full of water, and even if it emptied the pilot light shouldn't give it any problems.
-- John Stumbles -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+ procrastinate now!
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