My heater won't get hot after I flushed radiator?

let's make sure the heater hoses entering the firewall are hot when your rig is at operating temperature, if not, it's possible the heater core is stopped up (no circulation) taking the hoses loose and pushing water from your garden hose in both directions thru the core may unstop it ('course, you said you had checked it already)

i'm banking on your hoses being hot, and the above procedure is not necessary! there are blend doors within the hvac unit that may be "stuck/ broken/ or the actuator just ain't-a-workin' to move them"

With a large (ain't i pretty!) hand mirror and a good flashlight, you may be able to see the actuator (and whether it moves or not) when you move your controls.

i hope this aids you

let us know how things are working out!

the medic

You could have air trapped inside the heater core which should work it way out after divers for a few miles, if not jack the front of the car up and run the engine this will help burp the syte,. also please go over this video it can help

https://www.youtube.com/watch?v=SNRb6pSwYuU&t=1s

Let us know what you find.