On 13/03/2018 08:04, RJH wrote:
How long is it 'safe' to leave a system drained?

I drained the sealed 12 radiator combi system down completely yesterday,
isolating only the boiler, meaning to add a radiator and replace a
couple of others. However, the job has taken longer than I planned, and
work/drinking commitments mean I've not got that much time. I could lash
it all back together this evening, but that wouldn't get the jobs
finished how I'd like.

Would leaving it until Friday present a high risk of corrosion etc?

The fresh air in steel rads may cause some corrosion, but it will be a
miniscule amount - the surface area of the steel is big, the amount of
available oxygen is small, and even if it were all used up, won't
readily be replaced, even with the bleed valve open.

Cheers
--
Clive