The washing machine inlet screen is the small mesh disc sitting where each fill hose meets the machine. It exists to keep grit and pipe scale out of the fill valve, and when it blocks the machine fills slowly, fills on only one temperature, or reports a no-water fault while the tap is plainly open.
Where the screen actually is
There are usually two, one behind each fill hose connection at the back of the machine, hot and cold. On many models the screen sits inside the machine's inlet port and can be lifted out with needle nose pliers; on others it is pressed into the hose coupling itself. Some homes also have a screen in the faucet outlet. Check all of them, because a machine that fills slowly on one temperature has told you which side to open first.
Cleaning it without causing a flood
Close both supply taps and pull the plug before anything else. Have a towel and a shallow tray ready, since the hoses hold water even after the taps are shut. Unscrew the hose, ease the screen out, and rinse it from the clean side outward so the debris comes back the way it went in. A soft brush and a soak in white vinegar lift scale. Refit the screen the right way round, hand tighten the hose, then open the taps and watch the joint for a minute before you push the machine back.
What the debris tells you
Look at what came out. Fine sand or silt on a well points at a failing well screen or a missing sediment filter upstream. Rust flakes point at galvanized pipe or a corroding water heater on the hot side. White crumbly grit is scale from hardness. Black rubber fragments are the inside of a perished hose, which is a warning worth acting on: a hose that is shedding material is a hose that is close to bursting.
Stopping it happening again
A screen that blocks repeatedly is doing a job something upstream should be doing. A sediment cartridge on the laundry supply catches the grit before it reaches the valve and is far easier to service. For scale, the USGS defines hardness as dissolved calcium and magnesium, at soft up to 60 mg/L, moderately hard 61 to 120, hard 121 to 180 and very hard above that; the harder the band, the more deposit accumulates in valves and heating elements. And while you are back there, fit braided stainless hoses and note the date.
Questions people ask about washing machine inlet screen
Can I run a washing machine without the inlet screen?
You can, but do not. The screen protects the fill valve, and a single piece of grit can hold the valve open and flood the machine.
Why does my machine only fill with cold water?
Most often the hot inlet screen is blocked or the hot supply valve is partly closed. Check the screen on that side before suspecting the valve or the control board.
How often should the inlet screens be checked?
Once a year is plenty for most homes, and more often on a well or after any plumbing work that disturbs sediment in the pipes.