The short answer
On a built-in that drains through a waste disposer, the commonest cause is something that should have been done on installation day and was not. Ranked first on this platform: A disposer knockout plug or a blocked air gap. The checks below follow that ranking, and the first of them need no tools and no panel removed.
What you observe
- It has never drained properly since the day it was installed — A machine that never worked is an installation fault, not a failure.
- 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.
- NEAR MISS — a little water in the sump at the end of every cycle — A small amount low in the sump is normal and keeps the seal wet. Standing water above the filter is not.
Causes, most likely first on this platform
- 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 ranks first on this platform because a plug inside the disposer inlet has to be knocked out when the machine is connected, and a machine that has never drained properly since the day it was fitted is almost always one where nobody did.
- 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 second here because this is a premium built-in appliance set flush into cabinetry, so the installation is a variable in every fault and service access is through the front.
- 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 third rather than higher: real on this platform, and less common than the causes above it.
Check in this order, and why
- Check the disposer inlet and the air gap on the worktop — Both are outside the appliance and both are quick to look at. It leads because it tests the top-ranked cause.
- Lift the filter out and look into the sump below it — Free, immediate, and it is the leading cause. Tests the second-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 third-ranked cause.
What an owner can safely check
- Take the cap off the air gap and clear it, and confirm the disposer inlet is open — Both are two-minute jobs with immediate results.
Tools: screwdriverAbout 20 min
- 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
- 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 Monogram 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.
