My Ender2 v3 heating bed keeps heating up even set on 0.
The temperature is being read so it can’t be the thermistor right?
I have used a new motherboard, power board and a new display module complete so I’m at an impasse as to what it could be.
Please help Obie Wan you’re my only hope lol.
One possibility. If the thermister is bad, not reading right or just to low, it will give a false reading as if the temp is to low. The controller continues to add power to the heater trying to get the bed temp up to were it thinks it should be. This is one type of thermal runaway which can be very dangerous.
Another possibility is that the part of the MB which controls the thermistor is not working right and even though it looks like it is set to Zero it is not.
Other then that I got nothing.
There was this one time that this guy I know* did something really dumb and plugged the bed heater wires into the power in on his main board and the psu 24v into the bed heater output terminal. When the printer turned on the display looked normal but the bed would start heating right away and wouldn’t stop.
I’m assuming you likely didn’t do that but thought I’d throw it out there just in case since you mentioned changing boards.
*the guy may have been me.
I’d double check all the wiring. I might be a thermiresistor but I don’t see how it could fail and still want to heat when at not told to.
I’ll have to check with my multimeter, thank you for the suggestion. 
I don’t think so, I was afraid of wiring it wrong so meticulously followed from pictures I took before I disassembled. I’ll recheck though thank you. 