title_body: Keurig K155 intermittent water level detection failure
upvoted_answer: Most coffee machines use magnetic water level sensors. I do not see a reason why Keurig does not have.
  
  You may see the basic idea on this page, I copy the animation here to make it easier to understand. So, it is normal that there are not any visible parts, as it is magnetic.
  
  
  
  So, let's focus on your problem. These kind of levels may broke for some reason from time to time. Electrical discharge, strong magnetic field near-by, and so on. I suspect that this sensor is partly broken; it cannot correctly measure the magnetic field. If this is the case, cleaning probably will not fix your problem and you need order new parts.
  
  What you can do? You may try to trick the sensor with a magnet. I cannot think that it is practical if you cannot really build a working mechanism for daily use.
  
  Still, I strongly advise coffee machines to be cleared regularly. At least, mold may grow inside.