Re: Bed is warped--concave upwards
I would just check the outer 4 posts, or if you have any old motherboard washers, place them under the middle two fixings, to raise it up. I did mine on one edge. I do notice after along print at high temps, areas with no fixings can drop minutely, and a gentle pull brings them back to square. I figure that removing a well stuck model can cause the same affect, so always check every week, all is square.
Re: Bed is warped--concave upwards
My bed is warped too! It seems as if the middle two spacers need to be higher.
At first glance I thought some screws might be too tight or loose but after some fiddling I removed the bed and placed it on a flat surface.
This explains why larger prints won't work. (Z is adjusted for the middle which works fine but the edge obviously won't stick)
Is this a warranty issue or do I have to try and put some washers in the middle?