Boiler seems empty, not sure why?

So I usually flush the rusty water out of the gas boiler once a month or so, just run it until it’s clear. I went to do that today and nothing came out and the water fill glass was empty. Boiler has an automatic refill which had both a green and red light lit up and it didn’t kick on to refill.
Obviously the boiler isn’t being used now but any ideas what the issue could be?
And can I leave it as it until our pre-heating season servicing or could it cause issues by leaving it completely empty for next few months?
If helpful, it’s a gas boiler for a 1-pipe steam radiator system. Thank you all for any advice!