@infiniteloop
As soon as I trigger the bed heater, a reset happened. But in the meantime I made some tests with another power supply. I hadn't already done that, because I know it is not powerful enough, but that's a nice lab power supply, with appropriate protection so I decided to have a try because I happened to have a doubt on my usual one. As expected, it does not work but there is no reset, there is only an undervoltage error in the Duet GUI. So I presume my power supply was damaged when the initial bed heater overheated. The old power supply is a 10Amps, and the protection fuse is 15A, so... I ordered a new power supply, I'll report here. In the meantime, standby, and thanks for your attention.

@infiniteloop
As soon as I trigger the bed heater, a reset happened. But in the meantime I made some tests with another power supply. I hadn't already done that, because I know it is not powerful enough, but that's a nice lab power supply, with appropriate protection so I decided to have a try because I happened to have a doubt on my usual one. As expected, it does not work but there is no reset, there is only an undervoltage error in the Duet GUI. So I presume my power supply was damaged when the initial bed heater overheated. The old power supply is a 10Amps, and the protection fuse is 15A, so... I ordered a new power supply, I'll report here. In the meantime, standby, and thanks for your attention.

Hi, I have a small "Microdelta" printer that was retrofitted with a Duet 2 Wifi. It has been running fine for years, but recently it started resetting when setting the bed heater on. I unmounted the bed heater, which is the polyimide film kind. Part of it was unsticked from the bed surface, with overheating signs. I thought it was the cause of the spurious reset, and chose to replace it with a 120mm 55W / 12V silicone heater. But the spurious reset is still there. Any idea of what I should check ?