Heater stops working. it comes on and off.. - 1998 Pontiac Bonneville

Your front blower motor has a problem. Locate it and with the blower on, hit it. If it comes on then replace it.

You have a vacuum leak or a vacuum check valve has stopped working

Sounds like a bad heater switch.
Maybe loose wire that feeds the heater motor.
OR the blower resistors is making and breaking the circuit.
Possible bad heater motor. Try smacking the lower right dash panel when the heater is is in the "ON" position.

Find the heater motor first.TAP on the motor-if it goes then ,the heater motor is most likely faulty with burned brushes,inside.

Make sure your fan is working properly. When you turn on the heater you are forcing the fan to cool the radiator. It may not be turning on automatically when it is supposed to. Let us know if this helps..

The heater resistor has probably gone out. It should be located in the blower housing.

u need to change the ac/heater control panel.

The blower resistor will burn and smell without blowing a fuse

the stop leak has clogged your heater core. you may be able to flush it out if there is still some flow, otherwise heater core will need to come out.

Most likely the heater motor. To check tap the heater motor with it switched on if it starts blowing then thats the problem. to fix it's best to replace it I have tried to fix them and will work again until the next bump then they stopped again. It could also be a bad connection but this is unlikely as it won't come on at any setting. Cheers

the heater stops working then as you are driving the heater might start working. it comes on when it wants to it was working all summer it seems to stop working in the winter.when it strts getting cold outside that is when it starts acting up.