Parts & Components
Spray Arms and Jets: Why Wash Performance Fades
May 19, 2026 · 6 min read · Dishwasher Cleaning technicians
Wash quality declines gradually as jets narrow with scale. Clearing them restores performance more than any product will.
Short answer
Remove each spray arm, hold it to the light, clear every blocked hole with a straightened paperclip, flush it under a tap, and refit. Do this twice a year, more often above 10 grains per gallon.
How the spray system works
A dishwasher has two or three spray arms — lower, upper, and on many machines a small ceiling jet. Water is pumped through them under pressure, and the angled holes create the reaction force that spins them. Coverage depends on both pressure and rotation, so a partly blocked arm loses twice: weaker spray and slower spin.
The holes are small by design. Narrow them with mineral scale or a seed lodged inside and the pressure distribution changes across the whole arm.
Removing and inspecting them
The lower arm usually lifts straight off or unscrews via a central nut. The upper arm is typically held by a plastic collar you turn a quarter and drop. Take a photo before disassembly if you are unsure how it goes back.
Hold each arm up to a light source and look along the row of holes. Blocked ones are obvious. Also check the arm for cracks and for the hub seal — a cracked arm bleeds pressure and no amount of jet clearing will fix it.
Clearing and testing
Straighten a paperclip and push it through each hole. Do not use a drill bit or anything that can widen the hole — the spray angle matters. Then run water through the arm from the hub end at the tap and watch every jet produce a stream.
Refit, then spin both arms by hand. They should turn freely with no contact against racks or dishes. If an arm catches on a tall item, that item is the reason your top rack is dirty.
Preventing repeat blockages
Two things block jets: mineral scale from hard water and food debris that got past a dirty filter. So the prevention is the same maintenance stack — keep the filter clean and descale on an interval matched to your water hardness.
In very hard water we clear jets at every service, because at 15 grains per gallon a jet can measurably narrow within a year.
Frequently asked questions
- Why is only my top rack dirty?
- Almost always the upper spray arm: blocked jets, a blocked feed tube at the back of the tub, or a tall item stopping it from spinning.
- Can I soak spray arms in vinegar?
- Yes, a warm vinegar soak loosens light scale. Still clear the holes mechanically afterwards.
- Should the arms spin fast?
- They should spin freely by hand and rotate steadily under pressure. Sluggish rotation means blocked jets or a worn hub.