Yup, some buses have a electric booster pump to get the coolant circulating through the heater cores.
This is due to system restrictions that a plumber would call "head".
The multiple heater cores, and all that heater hose cause the engines water pump to bypass the heater lines, and circulate through the radiator due to the large hoses, and lack of restrictions.
"Don't argue with stupid people. They will just drag you down to their level, and beat you up with experience."
Patently waiting for the apocalypses to level the playing field in this physiological game of life commonly known as Civilization