Ok so my heat stopped working and I can't find the cause. I've already done the easy thing and changed the t-stat which changed nothing.

When the car has been driving for over a half hour it will blow warm air for about 30 seconds before getting cold. The only thing that I can think of thats related is a coolant housing on the back of the head was leaking. I fixed the leak but still no heat.

Any ideas on what I can check?

 

Clogged heater core, just flush it out.