Only COLD water in washing machine

Only COLD water gets into the tub. (Hot water comes out of the hot-water hose and cold water comes out of the cold-water hose).

The water inlet valve is less than 9-months old: both screens are clean, the passages look clean and the continuity tests OK. Can the water inlet valve be mechanically defective?

If the water inlet valve is working correctly, what other part(s) might be causing the no-hot-water problem?

try reversing the water lines at the home shutoff and see if only hot water enters

I will do that.

If only hot water then enters the tub, does that mean the inlet valve is bad? Or might another part be the culprit?

I will suggest that it is the valve or the circuit controlling the valve. Looking for voltage at the hot water valve should tell you which . I wish I knew for sure what voltage you should look for.

I believe most inlet valves are 120 volts.

check for 120 at the hot side

The ones I've seen have all been 120V too. And even if it;s not, whatever voltage is on the side that works should be on the side that doesn't when that water is called for. Sounds like either a bad solenoid valve, even though it's new, or a loose wire.

The water temp selector switch may also be defective (I assume it is not set to cold-cold now).

Look for a schematic stuck to the back or rolled up and stuck in the bottom or taped inside an envelope inside the timer/electronics compartment. It should show you what controls the valve. I.e. the schematic is often not in the owners manual but hidden inside the appliance