Pronterface measures the bed temperature when the power is turned off but 0 degrees when turned on


Around the time the lcd stopped working, it was showing 0 degrees for the bed and extruder and triggered a mintemp error. I replaced the thermistors but it didn’t help. I found if I heated the bed with a heat gun beforehand, I could get around the error and actually got a couple prints this way. But it’s not working anymore and I noticed pronterface reads the temperature correctly when the power is switched off but as soon as the power turns on, the reading drops to 0.
Any idea what the problem could be?


Just if I wasn’t clear, here’s a grab of the temperature graph. The initial line is with the printer turned OFF. When the power is on, the bed temp drops to 0 and it won’t let me preheat. Could this be a board issue? Maybe it’s tied to the lcd not working?