thermal runway on heatbed
the heat bed is heating one minute reads 60 next it reads 24. it goes back and forward from the two temps till it says thermal runway, I have checked all the connection's, and they all look good. so what do I do ,buy new heat bed or control board or both
any help please.
chappy
Re: thermal runway on heatbed
24 C sounds suspiciously like room temperature. Check carefully to see if the thermistor under the bed is well attached and in good contact with the bed. If it's falling away and then going back into contact as the bed moves, it might create the transitions you are seeing.
On the other hand, if those transitions between temperatures are "instantaneous" and if the thermistor is still attached to the bottom of the heater, then your problem is almost certainly fatigued wires to the thermistor. They can break internally (the copper conductor inside the insulation) if they are bent back and forth repeatedly at a single point. You don't need a whole new heat bed to fix this problem, but you need someone who knows how to splice in repairs to the wires. And then set the cabling up so you don't get fatigue failure again.
There are other possibilities, but those are the two I'd check first.