I come back an hour later - the heated bed is not getting hotter than 103°C, so the print has not started. I watch - no change in temperature.
I eventually discovered that my room ventilator fan is blowing against the wall seven feet away, and this is reflecting off the wall back onto the M2 bed (another six feet or so), not counting vertical displacement, but blowing strongly enough that the bed temp can't get over 103°C. I turned off the ventilator, the temp climbed to 110°C in a matter of seconds, and the print started just fine....
This makes me start thinking about enclosures....
