Hi, I've checked water inlet hoses and hose beneath unit. I’ve replaced the cold water inlet valve and the pressure switch. The water lines to the washer are brand new since we just installed the plumbing for this washer/ dryer. The machine works fine on the Rinse/Spin cycle selection. What is the diagnosis for this? Whirlpool model: wfw9151wy00. Thank you.

Ok so on that model it does have two separate valves for the hot and cold water intake. The issue you are having is that you replaced the wrong valve. The rinse cycle works fine because rinse only uses cold water and that valve is good. When you first start the washer it uses a mix of hot and cold water from the two separate valves so the hot water valve is bad and causing the fill to take too long on the first fill of the cycle. Replace the hot water valve and it will be fine. The valve for your model is linked below: