[batmmannn]

What Cre says goes but with mine, I had to open the heater valve before my heater hoses even got warm past the valve. My Valve was stuck closed. I didn't have any flow back to my heater core till I opened manually the valve. Once I opened the valve a big volume of air came out. Like Cre said likely your valve is bad. It should open when using heat and close when using AC.

My car overheated till I did these things, it didn't work itself out but rather air caused coolant in the overflow to boil out. I suppose in time it might have worked out, but where would it go? Out the coolant overflow? The coolant is a sealed system except when the pressure and heat open the radiator cap valve, by then I was low on coolant escaping to the overflow bottle as boiling fluid and steam. We all know how Toyotas react to low coolant. They get real angry and pissed off when their short on coolant.