[Paul]

Makes no difference in principle, but the water would be hot so be careful not to burn yourself on both rad and any water that comes out.

[Sao]

My plumber always turns the boiler off and does it in the summer months.

If you mean take the air out of radiotors yes I do it with the heating on. If you never did it, make sure to ask a professional to show it to you first.

[Kevan]

Better really to do it with the boiler running, as the pressure will be there, to force any air out better, just be careful when the water starts to spurt out of the bleed vavle, make sure you have a cloth under it to catch any water that comes out.

[Author]

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