A dishwasher isn't magic: it's a self-circulating water pump. Food recirculating back onto your dishes doesn't mean the machine is old — it means the filter is feeding dirty water back to the plates. Clear the route, and everything comes out clean.

Where the water goes (a dishwasher is a self-circulating pump)

A dishwasher doesn't "soak" dishes clean — the pump pressurizes water and fires it through the spray arm holes. Water is drawn from the bottom, shot through the holes at your dishes, falls back down — and passes through the filter on its way back. So poor cleaning has exactly three accounts: the filter at the source is clogged (dirty water recirculates back onto the dishes), the spray arm holes along the route are clogged (water can't reach one zone), or the route is blocked by the dishes themselves. All three are water-route problems, not an aging machine.

Match the evidence

• Everything's dirty — food bits on nearly every piece, gunk pooled at the bottom → Clogged filter: twist out the round bottom filter, rinse under warm water with a soft brush, seat it back, then run one empty cleaning cycle. The #1 cause — and a monthly maintenance item by design.
• One fixed zone — the same few pieces on one side of the lower rack, or up top, never come clean → Clogged spray arm holes: pull out the lower rack, lift the arm off, clear each hole with a toothpick, soak mineral scale in white vinegar, and spin it by hand after reinstalling — smooth and silent means seated right.
• Just a few pieces — exactly the ones nested together or hidden behind the big pot → Loading: dirty faces toward the spray, no nesting, large items to the sides away from the dispenser — then hand-spin the arm to confirm nothing blocks it.

Two counterintuitive habits: skip the pre-rinse — scrape off big chunks and load; enzyme detergent needs a little soil to grab onto, and pre-rinsing actually makes cleaning worse. Hot enough water — detergent needs 120 °F (49 °C) to dissolve; if the interior is bone-dry and cold after a cycle, heating has failed, and the detergent never worked at all. One honest limit: filter clean, arm spinning, loading right — still dirty — the wash pump impeller is weak (the cycle sounds duller than usual, with a hum), or the inlet valve is clogged (it hums while filling but little water enters). A tech comes with parts.