Drain Central Heating System- when is it safe to switch Boiler back on

[Topslice]

Drain central heating system (water tank in loft) in
a two storey house - ground and first floor
when is it safe to switch the boiler back on -
is it only when the tank in the loft has stopped making
a noise - implying that the system is back to where it
was before the system was drained.
The noise is the tank refilling with water after the stopcock
has been opened.

Also:
which rads drain first - is it the first floor
which rads fill first- is it first floor

Thanks in adavnce

 

[Deleted member 120897]

Drain from the lowest point if you’re draining the whole system, then after a while open upstairs bleed vents, which will leave you to drain each ground floor radiator in turn.

Upon refilling the system, close all vents, then bleed all ground floor radiators then upstairs (1st floor).