How to bleed radiators - Oil heating system

I read this, which has some other useful tips by the way:

[broken link removed]

This part confused me:
To bleed the radiator, turn off your heating and let the radiators cool. Then put your ‘bleed key’ into the valve at the top of the radiator and turn it to release the air. Be warned, water may escape once the air is released so you might want to have a cloth or towel, or even a jug to hand!

I thought you were supposed to bleed rads with the heating on, so that the pressure was built up inside them?
I have looked on the web and there seem to be different opinions on whether it should be on or off.
Some say the rads should be cool, some say hot (but with heating actually turned off prior to bleeding.

Any thoughts?

Most ( maybe all) oil systems are not pressurised, so you bleed the radiators with the heating off. I have done it many times.

In my experience, I don't think it mattered much if the radiators were hot or cold.

Gas systems are different, so you may have received conflicting advice from someone who assumed gas.

I always bleed the radiators when the heating (oil ) is on.
As I release the air I can feel the heat rising to the top of the radiator.
I close the valve just as the water begins to flow out.

All heating systems are pressurised, whether from a feed cistern or mains fed. It's best to vent your radiators with the system on as hotter air tends to rise and find it's way to radiators.
You should also start the venting process with the radiators furthest away from the heat source and then work back, keeping a towel handy to stop vented water spills that will stain.
Remember to top up your system if you have a mains fed sealed heating system (oil or gas). Gravity fed systems with feed cisterns will fill automatically.

Always better bleed with the system turned off, pump can cause air to be drawn into the system or move it as soon as you open the bleed valve, start at the top of the house and work down

My point exactly... So many contradicting views :-(

Thanks DGOBS.
That makes sense now.

There is no sure and fast way. I am sure you are not venting a whole system, just a radiator.

You need to find out does you system automatically refill itself or not. If it doesn't you may have to top it up after venting.

Vent the rad, if air comes out, followed by water, job done. If no water comes out, turn off heating and try again.

As I said, every system is different, but you just opening the vent a crack will normally be enough to vent a rad. Simple.