Start here
A Koolmore dishwasher holding water is telling you the path out is restricted. Begin with the filter stack packed with food debris, then follow the water outwards to the sink. Listen during the drain phase as well: a pump that hums but shifts nothing tells you something different from a pump that is silent.
What you observe
- Water backs up into the sink when the machine drains — A shared waste line or a blocked sink trap, not a dishwasher fault at all.
- A humming sound during the drain phase with nothing leaving — The pump is being asked to run and cannot move water — a jam or a blockage downstream.
- An inch or so of water left in the bottom at the end of every cycle — The classic signature. A small amount of clean water in the sump is normal on some machines; a standing pool is not.
- NEAR MISS — the machine will not start at all — No cycle and no lights is a power, door-latch or control fault, and a different page covers it. Drainage faults happen at the end of a cycle, not before it.
What actually causes this, ranked
- The filter stack packed with food debris — The filter is the first thing water passes on its way out, and it is designed to catch exactly the debris that will block everything downstream. Left uncleaned, it fills, water cannot get through it, and the tub stops draining even though the pump is fine. Ranked first: the failure rate is highest here and the test is free, so it is where the diagnosis starts. Commercial equipment is specified for throughput, so the causes that rank high here are the ones throughput drives: loading, supply and cleaning routine.
- A slow household drain backing up into the machine — A dishwasher shares its waste with the sink beside it, so half of this fault can live entirely outside the appliance and no part fitted to the machine will touch it. Second on the list — a real suspect, and the next one that can be settled by looking rather than measuring.
- The sink waste spigot blocked with debris — Where the drain hose connects to a waste disposer or a sink spigot, there is a small opening that blocks readily, and on a newly fitted disposer there is a knockout plug that must be removed before the dishwasher can drain at all. It sits here because it is a genuine cause with a narrower set of circumstances behind it.
- Drain pump jammed with debris or glass — The drain pump sits under the sump and pushes water out through the hose. A small object that gets past the filter — a fragment of glass, a cherry stone, a plastic tag — can stop the impeller dead, and the pump then hums without moving anything. Last, and the reason the order matters: it is the least likely of the four, and the three above are quicker to settle.
Check in this order, and why
- Scoop the standing water out and look into the sump under the filter — Glass, labels and fruit stones collect there and go unnoticed while the filter is in place. Start here — it is free, and it decides which half of the list you are in.
- Fill and empty the sink beside the machine and watch how fast it clears — A slow or gurgling sink is a plumbing fault and it explains the dishwasher complaint entirely. Then this — it is the next cheapest thing that can be wrong.
- Disconnect the hose at the waste spigot over a bowl and look into the opening — Grease and debris build a ring at that fitting that closes it down gradually. Third, and only if the two above found nothing.
What to do, step by step
- Remove the filter stack, rinse it under a hot tap with a brush, and refit it locked home — A filter left a quarter turn short of home lets debris bypass it straight into the pump.
Tools: washing-up brush, clothAbout 20 min
- Run a hot flush through the sink waste before re-testing the machine — Grease that has narrowed a branch responds to hot water long before it needs a rod.
About 15 min
- Run the sink tap and the disposer to confirm the waste runs freely — A sink that drains slowly will not accept a dishwasher discharge either.
About 10 min
- STOP if a step would mean defeating an interlock or a safety switch — Those exist to stop the appliance running in a state that can hurt someone. There is no version of this job worth bypassing one.
Before you open anything
Safety
Switch the dishwasher off at its socket or isolator before reaching into the sump or moving the machine — there is mains voltage inside the door panel and water in the tub, and the two only stay apart while the power is off. Wear a glove in the sump: broken glass collects there and it is not visible under standing water.
When to hand it over
Book a plumber instead of a technician if the sink beside the machine drains slowly or backs up when the machine runs. That fault is in the household waste and the appliance is simply the thing that noticed it.
Nearest pages of this class
What this page does not cover
This is the general page for the class rather than the page for your model. Where a family- or model-specific Koolmore page exists, it is linked here and it is the one to read first. Absent by design: part numbers, torque figures, wiring detail and anything else that differs between families.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
