Is it plugged into a Raspberry Pi running Octoprint or Astroprint? Something like that could override the settings. Alternatively I wonder if it’s set to preheat automatically for some reason? Have you navigated through the preheat options? You could try turning the extruders off. I take it the bed doesn’t heat up once the extruder has reached temperature?
The mosfet on the motherboard may have gotten zapped due to a short in the wire. They notoriously fail to the on position. You may be able to see the burned chip by looking at the motherboard.
I had the exact same problem, I know this is an old post but I want to leave a bit of advise to the people who might encounter this in the future.
Long story short I unwittingly shorted out the right heater cartridge and the mosfet burnt out. When I turned the machine on it started heating the right nozzle until it reached its limit and the printer turned itself off. When a mosfet on the board is letting current through you can see the corresponding led light up, most of the times when fets burn out they get stuck on the on position, so it lets the gate open for electricity to flow through and the led is always lit.
Repairing it was easy but you need to be patient and have a bit of soldering knowledge.
I got some FDS8812NZ 9fets since I couldn’t find the PSMN7R0-30YL 9 or IRF1413 7 fets readily available in my country. I researched the different models and data on them. Don’t just go buy any model, do your research and it will pay off.
You will need:
Any of the mosfets listed above or any model close to them (N-Channel 30V 10A, SOF-8 or LFPAK are good)
Soldering iron with fine tip 25-50W models work fine.
Soldering wire
Desoldering wire/mesh
Liquid or gel Flux
Plenty of light
Magnifying glass
The process is simple, you need to de-solder the burnt one and solder the new one.