@Phaedrux The machine has been running for 2 years with the same wiring, and there have been no changes to the cabling or the way the wires are routed. There has just been a change of thermal break and nozzle on the head.
There was no new appliance connected to the electrical network, no work (electrical welding or anything else), and no new machine installed.
It's very strange because it's perfectly reproducible: as soon as the temperature of the head reaches 386°C, the chamber sensor go to 2000°C, and as soon as I switch off the head heating, the chamber sensor start working again.
The chamber thermocouples are connected to the 6HC and the head thermocouple to a 3HC, connected to the 6HC via the CANFD bus.
We've already had problems with thermocouples, which we solve with filters. But this is really confusing.
That's why I'm thinking of a firmware problem... The machine was delivered with version 3.1.0, then updated to 3.4.5 about 8 months ago.
I can't manage to update to 3.5.0b4 to try, I don't have access to the SD board, I only have access to the machine's PC via Anydesk.
I think I'm going to have to travel to try and find out what's going on, it's 500km away but I can't leave the customer like that, he can't use the machine any more.
If you have an idea of something to try, I'd love to hear from you.