There would only be 2 scenarios that would make me resort to the kettle.
1) he’s already being violent and I’m struggling to fight him off
2) hes trying to rob me
The first would be worth the risk of a small splash back, the 2nd would be tipped straight over the back of his head when I told him my purse is under the bed (presuming that’s possible) either way if either me or my money is in danger someone is getting swilled
The backlash being from getting arrested/remanded in custody for pre meditated GBH, the splash back from boiling water/getting the hot kettle snatched off me, I wouldn't fancy either.
In the scenario of him being daft enough to rummage under the bed looking for the non existent money surely it would be a great opportunity to make a dash from the violent man?
In any event you never know how a situation is going to develop, there's usually no plan for an attack, but in close contact the best weapon is your own body, a swift tight grab to the balls, poke in the throat etc to give time to get away would be my thoughts, just remember not to put your finger in an attackers mouth though lol