I replaced a freeze plug because I only had water in it, not anti-freeze, and it froze overnight. No problem replacing the freeze plug, but now there is no heat even though the engine overheats. (Yes, I filled it with anti-freeze/water mix this time) I burped the system with a funnel attachment where the radiator cap goes, and got a lot of air out of the system. The heater hoses get hot, in and out , but still no heat inside.(Brand new heater core too) When I drive it, the engine overheats, with still no heat from the heater core. If it sits and idles with the funnel attachment on the radiator, it wont overheat, but when it idles or drives with the radiator cap on, it overheats and builds a lot of pressure inside the system. Still no heat either way.(even though the heater hoses are both hot. I sware I got all the air out of the system. Could this be a thermostat problem? Water pump is brand new too, and when I rev it up, the funnel attachment for bleeding the cooling system fills up more, so I know that is fine.

Help me out fellas:)