I'm wondering if you've got bad fuel, it does sometimes happen.

I'll be honest, I've never boiled water with just esbit or triox either, but I've gotten 20 ounces hot enough to make tea with, which to me means that there is a LOT of gas bubbles clinging to the bottom of the pan/pot, basically covering the metal below the waterline. I've also brought 12 ounces to a simmer if it is in a SMALL container, like an Olicamp cup, that has a cover, which can be enough to rehydrate your meal in some cases.

Use tablets for purification, esbit/triox for morale, warmth and tinder. That's my rule of thumb.