The hot water bottle is most probably passed its 'best by date', and you risk it failing and scalding your skin. The 'life span' of a hot water bottle is only 2 to 3 years, so be careful. (I posted a piece last week that explains how in the UK (and it may also work in other countries) you can check the age of your hot water bottle - https://medium.com/@nicksstories/the-retirement-newsletter-would-it-be-possible-to-turn-being-a-couch-potato-into-a-side-hustle-ac2c2d370199