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I've been asked to help out the local Science and Industry museum with their Orion. Someone previously replaced the ceramic resistors with a heater cartridge and some other work has been done by various people. They are a non profit and take whatever help they can get with fixing their 3D printers when they break.

The thermistor needs to be replaced. The Orion is an estimated year old version. The thermistor hole is larger than on the RostockMax V2. I have a spare EPCOS B57560G104F NTC 100kohm 1% thermistor. This thermistor didn't fit in the hot end for the V2 but does fit in the hot end for the Orion. I don't know which thermistor they had previously installed and neither do they. My concern is the thermistor table being off and causing print irregularities. Is it necessary to update firmware or is this the stock thermistor?

Without knowing what the old thermistor was and what it was set to it is difficult to respond.

But you probably should set the thermistor value in the firmware. Open the firmware and the code is well commented, it should become obvious immediately to which value you should set the thermistor table.

You can check prior to making up the hot end... Just plug your new thermistor directly into your Rambo Nozzle thermistor connector and turn on the Orion.
If your Nozzle temp is the same as your bed temp at room temp then your probably ok.

Just done it on mine and checked my thermistor this way before I made up the hot end with a new thermistor I picked up in the UK... was the same btw on mine.