Heater was working fine on the way to work and then was blowing cold on my way home twice. Took it in to be evaluated and shop said heater core. I’ve had no indication of smells noises or bad fluid. Picked up the car to take it to have a second opinion and that he worked as normal. He was blowing as normal to three days it was at the second shop. They did a heater core flush just in case. Picked up the vehicle with the heat working as normal but the next day In the morning when I went to go to work there was no hot air again. Temperature gauge looks good fluid looks good. Anybody have any idea???