Lava was never a fuel for boilers
If it was it would be stupid, because then, the lava wouldn't be consumed until ages have past (...it's lava, you don't have to burn it, it's not a fuel), and it can be obtained rather easily.
Plus if covert made it a fuel in boilers which is consumed, it wouldn't make sense, because (like stated previously), you don't burn lava as a fuel.
It's was but they nerfed to less than charcoal of looping. Which in my opinion is stupid. Charcoal is easier to get in one stop shop supply than lava (now a day a nether lake just doesn't cut it for mass power needs) So why on earth is lava less powerful than charcoal?? Charcoal is cheaper to fab than sinking 24k mj and a cobble or even 20k mj if your smart use the MFR one. It like saying "oh let's nerf coal to half of a charcoal". Doesn't make sense to nerf something that is harder to come by and at the same time making the easier to come by material better. TE already have Configs to change that if you hate power looping. (MFR does too) At least Fuel is left alone cause it's could lead to the same thing and just burn Ethanol instead of Fuel whenever they get rid of that 39% fuel looping. (even though it's involve doing other things that why PC doesn't care about feedback loops)