I'm an idiot. I'm brewing a pumpkin ale today, while also trying to get some work (for work) done. I was planning to fly sparge after mashing out. Not thinking, I dumped the entire mashout water onto the grains - not slowly or onto anything to protect the grainbed. Not a drop of wort would come out. I totally eff'd up the grainbed, even getting some grain in the short tube between my false bottom and the ball valve.
To salvage the brew, I had to dump the mash through a large strainer bag and sparge the grains through that. It'll probably be fine, but certainly not as efficient as I like. That's what I get for not paying attention. Lessons learned.