The heat sensor in the tub may be faulty. The heating element may be broken, but most of the time when this happens the breaker will through. If the tub has a circulation pump that is not working it will not close the in line flow sensor which will not alow the heater to come on due to low flow. Many flow sensors are clear and you can see it close when the system is running. check out these, and then replace whatever is broken.
If you spin your finger fast enough in the water in a circle you can make a whirlpool in the water. Or you could have some friends over and if you go in circles for a while (the more people the faster) then youll make a current and soon enough a whirlpool-AnswerMaster618-
If everything on your car ( thermostat, heater core, heat controls, water pump) has been changed and you are sure that it all works, check the water flow. A clog or an air bubble in the heat lines will cause coolant to not flow and have no heat output.
Lack of antifreeze or wrong mix of antifreeze and water.
Heat the water.
It could be low on anti-freeze/coolant. The coolant ratio could be off (especially if there is a leak and you have been adding water not 50/50). It could be the thermostat. It could be the water pump. It could be a plugged radiator or heater core. Begin with the least expensive and easiest and diagnose deeper until you find the problem.
Too much heat could dehydrate water and kill trees and plants.
water pump could be going out, could be low on coolant (leak in system), a stuck open thermostat, a plugged up heater core, temperature blend door may be faulty,
A couple possibilities are: low coolant level or bad water pump. just based on overheating and no heat, sounds like the thermostat is bad or it could be the water pump thermostat
a bad water pump could cause low heat. The heater uses the coolant from the pump to generate heat.
could be water pump or radiator or radiator cap try that if that don't work than you had to do something wrong on the head gaskets
A vacuum would retain the heat best, hence a thermos flask has a vacuum around it =-)
Either the thermostat or the heating element is faulty !