@minimaxer wasn't able to get back online last night but suspected PT100 as I had the same issue when converting an Up Plus 2 for someone an age ago.
Ok extra cost but the boards mount on Duets (post 0.6 or 0.8.5) with no extra hardware. PT100 are better sensors on many measures, but rely on a well shielded system. That said, if you are converting a machine like the ultimaker then shielding issues are likely already sorted, unless it is broken accidentally in the conversion.
Just keep an eye out for impossible heat changes on the temp plot. In other words if there are sudden changes of 5-10C or more in reported temp in an instant then you have wiring or noise issues.