Summary

"Not cleaning properly" covers several distinct symptoms that customers often describe the same way: a white/grey film on glasses, gritty residue on plates, food debris left on items, or dishes coming out merely damp rather than clean. Each points to a different part of the wash cycle — spray distribution, filtration, detergent chemistry, water hardness, or pump pressure — and misdiagnosing one for another wastes a visit.

The dishwasher wash cycle depends on four things happening correctly together: hot water reaching the correct temperature, detergent releasing at the right point in the cycle, spray arms distributing water under sufficient pressure to every item, and the filter keeping soiled water from being redeposited on clean dishes. A fault in any one of these presents as "dishes aren't clean," which is why a structured check — rather than jumping straight to "replace the pump" — saves time and avoids unnecessary parts replacement.

This is one of the most common non-emergency dishwasher callouts after drainage and leaking, and unlike those two faults, it is rarely caused by a single failed component — it's more often a combination of a dirty filter, low detergent dose, and hard water scaling that develops gradually rather than failing suddenly. That gradual onset means customers frequently assume the appliance is simply "wearing out" when the actual fix is a filter clean, a hardness setting adjustment, or a spray arm unblock.

Key Facts

Quick Reference Table

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Symptom Most likely cause Fix
Gritty/sandy residue on plates Filter not seated correctly, or badly blocked filter recirculating debris Remove, clean, correctly reseat filter assembly
Cloudy white film on glasses Limescale from hard water, or water hardness setting too low Check/set water hardness dial; check salt reservoir; consider a limescale/machine-clean treatment
Food debris left on some items, others clean Spray arm jet blocked on one arm, or item blocking arm rotation Clear jets with a pin/toothpick; reload to avoid obstruction; check arm spins freely
Dishes come out only lukewarm/damp, not properly clean Heating element or thermostat fault — water not reaching wash temperature Test element continuity/resistance; test thermostat; replace faulty part
Detergent tablet/powder still sitting in dispenser after cycle Dispenser flap jammed or mechanism failed Clean and free the dispenser mechanism; replace if the catch is broken
Streaky/spotty but otherwise clean Rinse aid empty or dispenser not releasing Top up rinse aid; check dispenser dial setting
Cleaning got gradually worse over weeks/months Progressive limescale or filter clogging Full filter clean, salt top-up, descale/machine-clean cycle
Wash cycle completes fine but pressure feels weak on inspection Circulation pump wear or partial blockage Inspect/clean pump inlet; test pump; replace if worn
Poor results only on eco/low-temp cycles Normal — eco cycles wash cooler and longer by design Confirm with customer this isn't a fault; recommend a hotter cycle for heavily soiled loads
Inlet water flow seems slow filling Water inlet filter or valve partially blocked Clean inlet filter; check valve if flow doesn't improve

Detailed Guidance

Step 1: Rule out loading and cycle selection before opening anything

Before any component check, confirm the basics that account for a large share of "not cleaning" complaints that aren't actually faults:

  1. Ask what changed — a new detergent brand, a change in loading habits, or a new water softener/filter installed on the property often coincides with the complaint starting.
  2. Check the load isn't overloaded or nested in a way that blocks a spray arm's rotation — spin each spray arm by hand with the rack removed to confirm free movement.
  3. Confirm the cycle selected suits the soil level — eco and 45-50°C cycles are designed to wash for longer at a lower temperature and will not match the results of a 60-65°C intensive cycle on heavily soiled pans.
  4. Check the water supply — a dishwasher fed from a combi boiler's hot outlet, or with an unusually low incoming pressure, may not be filling or heating as the manufacturer intended.

Step 2: Diagnostic tree

DISHWASHER NOT CLEANING PROPERLY
│
├── Check and clean filter assembly (every job, first)
│     ├── Full of debris / incorrectly seated → clean, reseat, retest
│     └── Clean and correctly seated → proceed
│
├── Check spray arms
│     ├── Won't spin freely when tested by hand → obstruction from
│     │     loaded items, or arm bearing/clip fault → clear/repair
│     ├── Jets visibly blocked (limescale or debris) → clear with
│     │     pin/toothpick, run test cycle
│     └── Spin freely, jets clear → proceed
│
├── Check water temperature reaching the tub
│     ├── Water feels cold/lukewarm during wash → test heating
│     │     element (continuity/resistance) and thermostat
│     │     → replace faulty component
│     └── Water reaches expected temperature → proceed
│
├── Check detergent dispenser and dosing
│     ├── Tablet/powder still present after cycle → dispenser
│     │     mechanism jammed or catch broken → clean/replace
│     ├── Dispenser empties correctly but dosing looks light →
│     │     confirm correct dose for load size/hardness, check
│     │     customer isn't cutting tablets or underdosing powder
│     └── Dosing and dispenser both correct → proceed
│
├── Check water hardness setting and salt reservoir
│     ├── Setting doesn't match local mains hardness → correct
│     │     the dial/electronic setting
│     ├── Salt reservoir empty or salt bridging → top up, break
│     │     up any bridged salt, allow several cycles to clear
│     └── Setting correct, salt topped up → proceed
│
└── Check circulation (wash) pump
      ├── Weak spray pressure at all arms despite everything
      │     above being clear → inspect/clean pump inlet, check
      │     for wear
      └── Pump confirmed worn/faulty → replace

Cleaning filters and spray arms

  1. Isolate the appliance at the fused connection unit before any hands-in-tub work.
  2. Remove the lower spray arm (usually a quarter-turn release) to access the filter assembly beneath.
  3. Twist and lift the coarse filter, then remove the fine micro-filter beneath it; rinse both thoroughly under a running tap, using an old toothbrush on the mesh.
  4. Check the sump area beneath the filter for glass fragments, bones, or labels before refitting — an incorrectly reassembled filter (fine filter not seated first) will recirculate soiled water and undo the clean immediately.
  5. Remove each spray arm and check every jet hole is clear; a pin or fine wire will clear most blockages. Hold each arm up to the light to spot partially blocked jets that aren't obviously visible.
  6. Spin each arm by hand once refitted to confirm free rotation before closing up.

This 10-15 minute check resolves a large proportion of "not cleaning properly" callouts without needing to test any electrical component.

Diagnosing a heating fault

If the filter, spray arms, dosing, and salt are all confirmed correct but dishes are consistently only lukewarm or damp rather than properly clean and dry, the fault is most likely the heating element or its control thermostat:

  1. Isolate power and access the heating element — usually visible at the base of the tub as a circular or U-shaped element, sometimes hidden beneath a cover.
  2. Test element continuity/resistance with a multimeter against manufacturer specification; an open circuit confirms a failed element.
  3. Check the thermostat and, on machines with a separate NTC temperature sensor, test its resistance against the temperature/resistance table for that sensor.
  4. If the element and sensor both test correctly, suspect the control PCB not switching the element circuit — this needs full appliance diagnostics against the specific model's fault code list, where fitted.

Water hardness, salt, and limescale

Hard water areas (much of the South East, East Anglia, and parts of the Midlands) see significant scale build-up inside dishwashers without an active, correctly-set water softener. Confirm the customer knows the local water hardness (their water supplier's website will state it) and that the appliance's hardness dial or electronic setting matches it. Check the salt reservoir is topped up and that salt hasn't compacted into a solid mass ("bridging") that stops it dissolving — break this up with a spoon or plastic tool if suspected. Where scale has already built up on the element and spray arm jets, a dedicated dishwasher descaler/machine-clean product run on an empty hot cycle will usually clear light-to-moderate scaling; heavier scaling may need the element removed and manually descaled.

When to recommend replacement over repair

Recommend replacement over continued repair where the fault is a circulation pump failure on a machine already over 8-10 years old, particularly if it coincides with other ageing symptoms (door seal perished, drain pump also worn, PCB showing other intermittent faults). A single filter clean, salt top-up, or spray arm unblock is always worth doing regardless of appliance age, since these are quick, low-cost fixes.

Frequently Asked Questions

The dishwasher is only a few months old and already leaving dishes dirty — what's different about a new appliance?

New-appliance complaints are most often loading habits carried over from the old machine (different spray arm layout, different rack spacing) or the water hardness setting not having been configured correctly at installation. Confirm the hardness dial was set for the property's actual water hardness during commissioning, and check the customer's loading against the manufacturer's guide before assuming a manufacturing fault.

Is it worth replacing rinse aid and detergent brand before doing any diagnostic work?

It's a reasonable first question to ask, not a fix to apply blindly. If the customer recently switched detergent brands or started using own-brand tablets, ask them to switch back temporarily as a diagnostic step — some cheaper detergents underperform on grease-cutting or don't dissolve fully in shorter/cooler cycles. This isn't a substitute for checking the filter and spray arms, which should be done regardless.

Can hard water damage cause permanent problems even after fixing the salt/hardness setting?

Yes, in some cases. Sustained scaling can permanently reduce a heating element's efficiency (though rarely enough to need replacement immediately) and can pit spray arm jets over years of neglect. Correcting the hardness setting and salt top-up going forward stops further damage, but existing heavy scale on the element may need manual descaling or, in severe cases, element replacement to fully restore performance.

How do I tell a spray arm fault apart from a pump fault?

A spray arm fault typically affects one zone of the load unevenly — items directly under a blocked jet or on the side an obstructed arm can't reach stay dirty while the rest of the load is clean. A pump fault reduces pressure across the whole cycle more uniformly, so the whole load comes out under-cleaned rather than one obvious zone. Confirm by spinning each arm by hand and checking every jet before concluding it's a pump issue.

The customer says the dishwasher is noisier than it used to be as well as not cleaning well — related?

Often yes. A worn circulation pump bearing, a partially blocked impeller, or debris caught in a spray arm can all cause both increased noise and reduced cleaning performance, since the same mechanical wear or obstruction affects water flow and creates vibration/noise. Investigate the pump and spray arms together rather than treating noise and cleaning performance as two separate faults.

Regulations & Standards