the whistle on the kettle keeps popping off
Given that PTFE (Teflon) tape is meant for use on drinking water pipes, and PTFE is used for non-stick cookware (which gets much hotter than a kettle spout), I'd happily use it (the type for potable water). 

Making a habit of consuming it probably isn't a good idea but flecks of non stick coating do sometimes get into food, without poisoning anyone. 

I've recently read a research paper suggesting that PTFE could be used to bulk out food as a weight-loss aid: Polytetrafluoroethylene Ingestion as a Way to Increase Food Volume and Hence Satiety Without Increasing Calorie Content.  I'm not sure I fancy it, and it would contribute to microplastic pollution - but the paper proposes PTFE making up 25% of foods, while the worst that could happen here is a few scraps.  They say it's safe. In rats.