Radiator cap needs replaced if it's coming out there, those caps are rated to a certain PSI but will fail over time. Heater core could be bad but would need more info. like what does your temp gauge say, if it never gets to the middle of the gauge then the thermostat is bad, if it's in the middle (operating temp) then the heater core is the reason you aren't getting heat. You may also have what's referred to as vapor lock, an air bubble trapped in your cooling system preventing the proper flow, make sure when you fill your coolant/antifreeze that you follow directions for your specific car as to how to bleed the system of any air. Hopefully you are only "flushing" out the system with the garden hose, 50/50 coolant (go by proper fluid for your make-gm,ford,etc..) or undiluted coolant mixed 50/50 with distilled water is the only thing that should be used while engine is running. Tap water will cause buildup and blockage of your cooling system by leaving deposits and promoting rust.

Does your cap have a small vent in? If so, make sure it's clear.

The pipes going to and from reservoir, are they clear and not clogged?

Did you bleed the air out of the system when you re-filled it with coolant / anti-freeze?

I do not see where you replaced the most obvious choice the radiator cap and the thermostat. The thermostat is most likely stuck. When you replace those flush the cooling system and refill with new coolant.

If you replace the cap and it's still overflowing, you've got a head gasket leak.

no further comment needed.

My car appears to be leaking out the cap of the water reservoir in quite large amounts when I stop, it might happen when I am driving as well but I do not know. Also no heat comes out the cab heater and the only time it does come out is when I rev the engine a lot like when driving up a hill. I have checked the head gasket and the oil its not white so yay. I also have to fill up the tank every day or every few hours if im at work as I am a delivery driver. I have also flushed the cooling system with a hose and the water was circulating out perfectly from the radiator and the cooling system in the engine.

If you need more info to give an answer then please state what you need and I will check.

Thanks in advance

Regards

Ben