Something is really wrong with my printrboard.
Looks to me like your Mosfet is blown. They can blow full-on or full-off and yours is blown full-on. This can happen if you short the pcb leads while the bed is on. If you’re handy with a soldering iron you can replace it yourself. I did mine and its worked fine ever since. Otherwise you need a new board.
How do I determine which component is the mosfet and whether it is blown? I have a Rev f4 printrboard.
Google mosfet and look at the images. Then do the same for Printrboard. It will be pretty obvious. They have 3 leads and are some of the largest components. Also, they are close to the hot end and heat bed connectors. HTH.
I think the fet layout is the same on the various boards (it’s the tall doohickey on the same side as the power connector in the corner position):
http://www.printrbottalk.com/forum/viewtopic.php?f=15&t=3003&p=20698&hilit=heated+bed+mosfet#p20698
If you decide to replace the fet yourself, let me know and I’ll send you one (I’ve got two extras).
Thank you @SirGeekALot , I think I know which one. @John_Davis , you sir is a gentleman. It looks like the printer is still working. I am printing something at the moment and the readings of temperature on octoprint looks as expected. I will definitely use that offer if it turns out replacement is needed.
That thread has awesome info on how to test a mosfet.
Its report of this in recent memory, but happy to replace the component if you need one. I love guys who can troubleshoot and solder!!
Brook
Thank you Brook. Turns out the Printrbot Simple Metal is more resilient than I thought. It finished a 10 hour print yesterday and another 10 hour print is being done as I speak. Coming home every day to find a completed piece is like Christmas morning every evening 
Nice!
@Dat_Chu With no intention to undermine one’s faith in Printrbot’s products intended, I personally would not leave a heated appliance running unattended unless it has significant fire safety measures built in (I don’t know of any consumer 3d printers that do this yet).
And by the way, the new Metal models from Printrbot are surely much safer in this regard than many other consumer/hobbyist 3d printers.
Certainly. I need to figure out a way to make sure it is fire proof.
http://www.soliforum.com/topic/6608/beware-your-3d-printer-they-can-cause-fires/
Some interesting ideas in this thread.
If I put my printer in the garage on top of a bunch of stone tiles away from everything else. It is fire safe but then my filament will get moistured. I think I need an enclosure with a built-in temp/smoke detector.
Maybe I can get an enclosure to store all the filament and route the excess heat from the heated bed to it.
Check to see if the heat sinks of the MOSFETs are not touching anything… even the other MOSFET. If they ground out, then they will turn on. I wound up putting heat shrink around mine to prevent that.