I actually saw and experienced these live and in person at a local festival last weekend. They are pretty cool.
That little button like thing one pic shows being pressed is what activates the heat. Once you are done with it, you boil the unit for 3 minutes to reset it.
I bought a handful of their hand warmers to use for outdoor sporting events. They get pretty hot and work well.
I bought one of these a few months ago, and after the first bath (to turn it back into liquid to be used again), I could tell it wasn’t going to last. The second bath killed it. I would be interested in seeing if as hot as you can get it tap water would work since I’m thinking it got too hot, but warning for this product for sure.
One of mine actually split at the seams this past weekend while being re-charged (in boiling water). Disappointed.
If it was still within the warranty period you should contact customer service.