So, boilers aren't working. Apparently, the developers updated the calculation of steam output from standard boilers. Currently, a boiler produces 30 steam and consumes 900 mW of energy, but a steam engine also produces 900 mW of energy for 30 steam. I tried to fix this by changing the parameters in the mod and even adding new block characteristics, but I didn't get far. As a result, as the boiler's energy consumption decreases, the steam output decreases. As the boiler temperature increases, the steam output decreases.

Oh, I noticed the mod description. It turns out the developer added the boiler only for crafting purposes, not for energy. Well, then it's not a bug, but a request to add steam output of at least 45 and make it at least usable for energy generation. Besides, using 900 mW for steam sounds very inefficient.