Martayeit

Hi guys I’ve recently been having problems with my cars coolant tank overflowing and becoming red hot. The heaters in my car are only blowing out cold air and do not heat up. I’ve tried running the car with the coolant cap off and seeing if it’s an air lock. I’ve replaced the coolant tank and still having the same issue. There’s no leaks anywhere on the car other than from the overflow. The temperature of the car is staying at 90 and doesn’t fluctuate. The cars temperature heats up within 5-10 minutes of driving. What could be the issue? pressure test has also been done on the coolant system and it came back fine