Dishwasher Not Cleaning Properly - What to Check in Barnet

Published October 2026 | Dishwasher Not Cleaning Properly

We asked our Appliance Repair engineers the questions Barnet homeowners ask most. If your dishwasher is finishing a full cycle but still leaving food residue, grease, or white film on your dishes, the cause is usually identifiable - and often something you can check yourself before calling anyone out.

Why is my dishwasher leaving dishes dirty even after a full cycle?

This is the most common complaint we receive from homeowners across Barnet, and it almost always comes down to one of four things: a blocked filter, clogged spray arms, incorrect loading, or a water heating issue. Dishwashers rarely fail suddenly - performance typically drops gradually, and many people don't notice until the problem has built up over several months.

The type of residue left behind usually points directly to the cause. A greasy film on dishes suggests the water isn't reaching the right temperature. Gritty or sandy residue in cups and glasses typically means the filter is blocked. White chalky deposits are almost always limescale-related, which is especially common in the harder water areas of Greater London.

Before booking an engineer, try the Voltrade GoFIX diagnostic tool. Describe what you're seeing - greasy plates, filmy glasses, unclean cutlery - and it can help identify the most likely cause before anyone comes out. Most dishwashers, whether it's a Bosch Series 4 or a budget Beko model, are built to last ten or more years with basic upkeep. A poor cleaning result usually points to maintenance, not replacement.

How do I check and clean the dishwasher filter?

A blocked filter is the single most overlooked cause of poor dishwasher performance. Many homeowners don't realise their dishwasher has a filter, let alone that it needs regular cleaning. It sits at the base of the tub beneath the lower spray arm and traps food debris to stop it recirculating onto your dishes during the wash.

Here's how to clean it:

1. Pull out the lower rack and locate the cylindrical filter assembly at the bottom of the tub.
2. Twist it anti-clockwise and lift it free. There's often a flat mesh filter underneath - remove that too.
3. Rinse both parts under warm running water, scrubbing with an old toothbrush to remove food, grease, and scale.
4. Check the sump area underneath. Remove any fragments of glass, plastic, or bone that could restrict or damage the drain pump.
5. Refit the filter and run a hot cycle to flush through.

Clean the filter at least once a month as a minimum. If you've never done it, expect it to take a couple of attempts to clear it properly. A heavily blocked filter doesn't just leave dishes dirty - it strains the pump and can lead to a more costly repair further down the line.

Could the spray arms be causing the problem?

Yes, and it's something a lot of people overlook entirely. Your dishwasher has two or three spray arms - one beneath the lower basket, one beneath the upper basket, and sometimes a fixed sprayer at the very top. They rotate during the wash, pushing water through small holes to reach every item in the load. If those holes get blocked with limescale, food debris, or detergent residue, water distribution suffers and cleaning performance drops noticeably.

Checking them takes just a few minutes. Twist or unclip the spray arms (usually without tools), hold them up to a light, and look for any blocked holes. Soak them in warm water with a splash of white vinegar for 20 minutes, then use a cocktail stick or thin wire to clear each hole individually.

Also check that nothing in the loaded machine is physically stopping the arms from rotating. A large serving spoon, a tall bottle, or an angled plate can catch a spray arm mid-cycle and halt it completely. This is a very common reason one rack comes out clean while the other doesn't. On Samsung and LG dishwashers, a cracked spray arm connection can reduce water pressure even when all the holes are clear - if cleaning alone doesn't solve it, that's worth flagging to an engineer.

Does water temperature affect how well the dishwasher cleans?

It affects it significantly. Most dishwashers are designed to run their main wash between 50 and 65 degrees Celsius. Below that threshold, grease and protein-based soiling from meat, egg, and dairy simply won't dissolve, regardless of the detergent you use. If you open the door during a cycle and there's barely any steam, or if dishes feel cool rather than hot when the programme ends, the heating element may not be working correctly.

A failed heating element is one of the more common mechanical faults our engineers see in Barnet, particularly in machines that are four to six years old. The part itself typically costs between 30 and 70 pounds, with repair including labour commonly running between 80 and 150 pounds - well worth doing on a good-quality appliance.

On some older Hotpoint and Indesit machines, the thermostat can fail rather than the element itself. The symptoms look identical from the outside, but the diagnosis and repair differ. Our engineers carry the right diagnostic equipment to identify which component is at fault on-site, and the Voltrade GoFIX tool can give a useful steer on what's most likely before you book a visit.

Am I using the wrong detergent or not enough of it?

Detergent choice and dosing have a bigger effect on results than most people expect. All-in-one tablets are convenient, but if you're running short or eco cycles, they often don't fully dissolve in time. These tablets are designed to release different cleaning agents at different stages of a longer wash - on a 30 or 45-minute programme, you're simply not getting the full benefit.

Check the detergent dispenser door too. It should spring open cleanly during the wash. If it's sticking or jamming shut, the detergent drops in too early and doesn't perform as intended. That's typically a simple mechanical fix and something homeowners rarely think to look at.

Rinse aid matters just as much as detergent. Rinse aid reduces water surface tension and helps water run cleanly off dishes, which is what delivers spot-free, streak-free results. Low rinse aid is one of the most common causes of cloudy or smeared glassware that people incorrectly put down to the machine or the water supply. Top it up and set the dispenser level to match your water hardness - the difference is usually noticeable within a couple of cycles.

Could hard water in Greater London be affecting my dishwasher?

Almost certainly, yes. Barnet sits in one of the harder water zones of Greater London, and limescale build-up is one of the most persistent causes of poor dishwasher performance in this part of the country. Over time, limescale coats the heating element (reducing its efficiency), blocks the spray arm holes, and leaves a white chalky film on glassware and crockery that detergent alone won't shift.

Most modern dishwashers have a built-in water softener that uses dishwasher salt - separate from your detergent and rinse aid. If you haven't checked the salt reservoir recently, do it now. It's usually accessed by unscrewing a cap at the base of the tub, near the filter. Refill with dishwasher-specific salt only - table salt will damage the softener.

Also check the water softener setting in your machine's menu. For most Barnet postcodes, a setting of 4 to 5 on a scale of 1 to 7 is typically appropriate, but you can verify your exact level through Thames Water's website. Running a dedicated dishwasher descaler every one to three months helps tackle the build-up that salt and rinse aid can't fully prevent on their own.

Why are my glasses coming out cloudy even when other dishes look clean?

Cloudy glasses are almost always caused by one of two things: limescale deposits from hard water, or etching. They look similar but the causes and remedies are completely different, so it's worth working out which you're dealing with before doing anything else.

Limescale cloudiness appears as a white film that wipes off when you rub the glass with a cloth dampened in white vinegar. If it comes off, you're dealing with a mineral deposit rather than permanent damage. Sort out your salt level, top up the rinse aid, and descale the machine - the cloudiness should reduce over a few cycles.

Etching is a different matter entirely. It's permanent micro-abrasion of the glass surface, caused by over-dosing detergent, very high wash temperatures, or regularly running light loads on intensive programmes. Etched glasses show a blue or rainbow tinge when held to the light, and the cloudiness doesn't wipe off. You can't reverse it, but you can stop it getting worse: use the correct amount of detergent for your load size, choose a cooler programme for lightly soiled washes, and use the "glass" or "delicate" cycle for finer items. Bosch and LG machines with dedicated glass programmes handle mixed loads well on this setting.

Does how I load the dishwasher actually make a difference?

It makes more difference than most people want to hear. Poor loading is behind a significant number of the calls we receive across Greater London, and it's often the last thing homeowners consider. The spray arms need a clear path to rotate, and water needs to reach every surface in the load. When items are packed in badly, entire sections of the rack can come out barely touched.

Loading habits that cause consistent problems include:

• Nesting bowls or cups together so water can't get between them
• Placing large items in the lower rack that block the spray arm from spinning freely
• Overloading so that items press against each other throughout the cycle
• Plates angled in a way that traps water in concave surfaces
• Tall items positioned where they obstruct the upper spray arm or top sprayer

The general rule: glasses and cups go in the top rack, angled down to drain. Plates and pans go in the bottom, facing inward toward the spray arm. Heavily soiled items should face the water source. Cutlery should be mixed in the basket rather than handle-to-handle so pieces don't nest together.

If your machine was cleaning well previously and has recently dropped in performance, check whether your loading habits have changed - it's often the first question our engineers ask.

When does poor cleaning point to a mechanical fault rather than a maintenance issue?

If you've worked through the maintenance checks - filter, spray arms, salt, rinse aid, detergent, and loading - and the machine still isn't cleaning properly, you're likely looking at a mechanical fault. The most common ones our engineers find across Barnet households at this stage are:

• Wash pump failure: reduced water pressure means the spray arms can't do their job. The machine may sound quieter than usual during the main wash, and items at the far corners of the racks will consistently come out dirtier than those near the centre.
• Inlet valve fault: a restricted or faulty valve limits how much water enters the machine. Less water means less cleaning power, and you may notice the machine takes longer than usual to fill at the start of each cycle.
• Control board issues: less common, but a faulty board can cause the machine to skip heating or rinse stages without any obvious error. This crops up more frequently in older Samsung and LG models with touch controls.

Repairs for these faults typically run between 100 and 250 pounds including parts and labour, depending on the machine and the specific component involved. Our engineers carry common parts for Bosch, Hotpoint, Beko, Samsung, and LG - and most repairs are completed in a single visit. If you're not sure whether you're dealing with a maintenance issue or something mechanical, the Voltrade GoFIX tool can help you work through the symptoms first.

Most dishwasher cleaning problems come down to maintenance rather than mechanical failure. Work through the basics - filter, spray arms, salt, rinse aid, detergent, loading - and you'll resolve the majority of issues without needing a callout. Where a mechanical fault is involved, it's usually well within economic repair range on a quality machine. Don't write off a good dishwasher without getting a proper diagnosis first.

How often should I clean my dishwasher filter?

For a household using the dishwasher daily, once a month is a sensible minimum. If you regularly wash heavily soiled pots, pans, or items with meat or dairy residue, cleaning the filter every two weeks will give noticeably better results and reduce wear on the pump over time.

Is it normal for water to sit at the bottom of the dishwasher after a cycle?

A small amount of water in the sump area beneath the filter is by design - it stops the door seal from drying out and cracking. However, if there's a visible pool of water covering the floor of the tub after the cycle ends, that points to a drainage fault and should be looked at by an engineer sooner rather than later.

Can I run my dishwasher on a quick 30-minute cycle for every load?

Quick cycles are designed for lightly soiled loads that have been pre-rinsed. Running a full load of dirty dishes on a short programme typically means the water doesn't reach the right temperature and the detergent doesn't have enough time to act properly. Use a full-length cycle for everyday loads and save the quick setting for items that are only lightly used.

Why does my dishwasher smell bad even after running a full wash?

Persistent odours almost always originate from the filter, the door seal, or the drain hose. Food debris trapped in the filter decomposes over time and the smell circulates during every wash. Clean the filter thoroughly, wipe down the door seal with a damp cloth, and run a dedicated dishwasher cleaner on a hot empty cycle to clear the drain path and internal components.