Even though the description says ranges of steam temperature will work, I found that you can't connect steam from tier 2 boilers (315°C) to the train. Tier 1 (165°C) works, haven't been able to test others. Otherwise cool mod.

what mod version are you using? can you give me your full mod list (with version numbers)?

https://i.imgur.com/PfipQgf.png
https://i.imgur.com/JkkXVSc.png
I did update bob's logistic / warfare / inserters since then, they were versions 0.18.8 / 0.18.4 / 0.18.2 when it didn't work

I was unable to reproduce the issue locally. Does it not refill at all or is it just the normal "cold" steam inside the locomotive?

I did some more testing and it turns out it probably has to do with the order of placing things down. If you connect the pump to the train and after that connect a pipe full of steam to that pump it wont insert steam into the train. But if you already have the pipe placed and then place the pump connecting the full pipe with the empty train it works.

correct - connections between pumps and locomotives are only created when the mod is able to determine the fluid type exactly. as the fluidTrains mod supports arbitrary fluids and not only steam this is still relevant. If you have an empty locomotive and a pump that is not connected to any fluid system, they will not connect because i can not decide what fluid to lock the locomotive tank into and connecting it to an incompatible fluid system would break things.

whenever the pump does not connect, you can just rotate a single pump twice and all pumps around the locomotive will update.