I like Nate too. He is known more for helping and protecting people than causing troubles. Therefore I doubt that it could be him as I can't find any reason for him doing it. Unless he knows anything about boilers and wanted to help to fix it and things went wrong.
I looked at the old video showing the possible culprit with some tools. He/she has got a glove and a black long sleeve, perhaps wearing a black jacket ? You can see it at 00:02 in the video in the link below:
http://www.digitalspy.com/soaps/neig...ath-trap-week/
I hope, the same way like you do, that it is not Nate. Hopefully Nate's exit is only temporary and he is gonna come back.