e73 - Sporadically it works fine and then shows e73 error on thermostat

[ShravanMacharla]

Hi, my thermostat is showing e73 error, I looked at the fuse and didnt trip it looks all good. It works sometimes randomly, and all of a sudden will show e73 error. 

[Patrick_Caezza]

@ShravanMacharla 

The E73 error means there is no power on the red (R, Rc, or Rh) wire, which can be caused by,

• a blown fuse
• condensate drain being blocked, tripping the safety switch
• furnace/air handler cover not being installed correctly, tripping the disconnect switch

These are just a couple of the more common causes