The short answer
On this machine the sump and the filter are cleared by hand, and on most of them that has not happened for years. Ranked first on this platform: A blocked filter and sump. The checks below follow that ranking, and the first of them need no tools and no panel removed.
What you observe
- Standing water above the filter at the end of every cycle — Water sitting on top of the filter names the blockage.
- It has not drained properly since the machine or the kitchen was worked on — A fault dated to a building job belongs to the building job.
- It has never drained properly since the day it was installed — A machine that never worked is an installation fault, not a failure.
- NEAR MISS — it drains but leaves dishes dirty — That is a wash-performance question and it is diagnosed from the filter and the arms rather than from the drain.
Causes, most likely first on this platform
- A blocked filter and sump — Everything the machine washes off ends up in the sump, and the filter is what holds it there. It ranks first on this platform because everything the machine washes off ends up in the sump, and a filter packed with soft food, labels and glass slows the drain to the point where the cycle ends with water still standing above it.
- A kinked drain hose or a missing high loop — The drain hose has to rise above the level of the tub and then fall, or the machine cannot hold what it has pumped. It ranks second here because a cabinet of this vintage has wear on everything at once, which changes the ranking: the parts that wear are far more likely than the parts that break.
- A disposer knockout plug or a blocked air gap — Where the machine drains into a waste disposer, a plug inside the disposer inlet has to be knocked out at installation and frequently is not. It sits third because the causes above it account for more of these cases, not because it is unlikely.
- The drain pump — A failed pump is silent, and a worn one runs without moving much. It comes fourth in the order — a genuine cause here, behind the ones above it on frequency alone.
Check in this order, and why
- Lift the filter out and look into the sump below it — Free, immediate, and it is the leading cause. It leads because it tests the top-ranked cause.
- Pull the machine out, or look under the sink, and follow the hose along its whole run — A crush or a sag is visible at once. Tests the second-ranked cause.
- Check the disposer inlet and the air gap on the worktop — Both are outside the appliance and both are quick to look at. Tests the third-ranked cause.
What an owner can safely check
- Bail the water out, twist out the filter, and clear the sump by hand — Glove on: broken glass in a sump is common.
Tools: jug, glove, clothAbout 25 min
- Straighten the hose and secure the high loop up under the worktop — Use the clip it came with, or a tie to the cabinet wall.
Tools: cable tieAbout 20 min
- STOP here — the remaining causes are diagnosed with a meter, not by eye — Record which of the checks above changed anything. That record is worth more to the visit than another attempt.
Before you open anything
Safety
Unplug the machine or switch off its breaker before removing any panel, and close the supply valve before disturbing a fitting. Broken glass in a sump is common: wear a glove and look before you reach.
When to call a technician
Call when the filter, the hose and the household drain are all clear and the machine still will not empty, because what is left is the pump or the control.
Nearest pages of this class
What this page does not cover
This page is written for the Moffat dishwasher as a class, not for one family or one model line. Where a family- or model-specific page exists for your unit, that page is the more specific answer and the one to read first. Deliberately not here: part numbers, wiring colours and disassembly order, which differ by family.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
