The answer, before the detail
On a Lagan dishwasher, a tub that will not empty is nearly always blocked rather than broken. clogged filter and sump screen is the likeliest point on this machine, and clearing it needs a cloth, a bowl and half an hour.
The symptoms, and the ones that mean something else
- The cycle seems to run much longer than it used to — Machines that cannot drain often extend the cycle while they try again, so a long cycle can be the first sign.
- 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.
- NEAR MISS — water is escaping onto the floor — Water outside the machine is a leak, and that page comes first. Deal with the leak before the drainage complaint it may be causing.
The ranking, and why it is this way round
- Clogged filter and sump screen — 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. On a badge this size the parts channel is thin, so the ranking is written around what can be checked and corrected without a part on order.
- The waste the machine drains into is itself blocked — The evidence is equally outside: a sink that gurgles or empties slowly has already told you where the restriction is before the machine is opened. It takes second place because the check is quick and because leaving it unchecked makes everything below it harder to read.
- Waste connection blocked, or a disposer knockout left in place — A dishwasher that has never drained properly since a kitchen change almost always fails here. A machine that drained fine for years and then stopped is more likely to be blocked at that same spigot with grease. It sits here because it is a genuine cause with a narrower set of circumstances behind it.
- An impeller stopped by something it swallowed — It sits low on the list because everything above it is more common, cheaper and reachable — but it is the cause that most often needs a part. Least likely of the four, and the one that only makes sense once the others are ruled out.
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. First, because it separates the top two causes in under a minute.
- 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. Second in order, and only worth doing once the first has come back clean.
- 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 in sequence — useful, but rarely where the answer turns out to be.
What you can do yourself
- 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 before testing anything electrical with the power on — The checks above are all done cold. A test that needs power applied is a technician test, whatever a video shows.
Read this before you start
Safety
Before anything is opened, switch the appliance off at its isolator and let the tub cool — a machine that has just finished a cycle holds water hot enough to scald. Mop up standing water before you kneel in front of it.
When this becomes a service call
Stop at the point where the next step means taking the machine out from under the worktop. Before that, everything is reachable from inside the tub and from the cupboard under the sink, and most of these faults are settled there.
Nearest pages of this class
What this page does not cover
A note on scope: this page treats Lagan dishwashers as one class. A page written for your specific family or model line will carry what this one deliberately leaves out — component locations, fastener sizes and the disassembly order — and it takes precedence over this page for your unit.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
