I think there's a mass transfer value somewhere, so you can see mass evaporated/condensed in a step. With UDFs there are a few places you can go wrong, so it's possible the UDF is trying to move mass from one phase to the other (according to your model) but the hook up isn't correct so nothing happens.
If you need that high a temperature, check material properties. Also, please confirm what boundaries you have inside the domain: how many fluid zones are there?
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