Asco Dishwasher: Will Not Drain
Standing water in the bottom of a dishwasher is almost always a blockage rather than a failed pump, and the blockage is usually in one of three places you can reach: the filter assembly in the sump, the drain hose behind the machine, or the air gap or waste connection under the sink. Asco sits one letter from Asko; once the machine is genuinely identified it behaves as a conventional appliance and rewards methodical work. Clearing the filter, the hose and the waste connection is owner work and it ends most of these. Replacing a pump is not.
What the owner actually observes
- Water stands in the sump above the filter at the end of the cycle.
- The machine hums at the drain step but the level does not fall.
- Water drains slowly and the last of it never leaves.
- Dirty water appears in the sump after the sink has been used.
- The cycle stops partway and reports a fault with water still in the machine.
- Not this fault: If the machine is draining but dishes are coming out dirty, the wash arms and the filters are the place to look. That is a different fault — see Asco Dishwasher: Does Not Clean or Dry (asco-dishwasher-cleaning-performance).
- Not this fault: If water is on the kitchen floor rather than in the sump, that is a leak instead. That is a different fault — see Asco Dishwasher: Water Leak (asco-dishwasher-water-leak).
Ranked for an Asco dishwasher
- A blocked filter assembly in the sump — Rank: first — Why ranked here: it ranks where it does because the filter is designed to be removed and rinsed by the owner, because food debris and grease build there faster than anywhere else, and because on a machine that has never had it cleaned it is blocked far more often than not
- The waste connection under the sink — a blocked spigot, air gap or disposer inlet — Rank: second — Why ranked here: a dishwasher discharges into the sink waste, and the spigot it connects to is frequently left with its knock-out plug still in place after installation or blocked with grease from the sink above it
- A different machine than the one being read about — Rank: third — Why ranked here: ranked here only because this badge is a single letter from another one; it costs nothing to rule out and it invalidates everything downstream if you do not
- The drain hose kinked, crushed or without a high loop — Rank: fourth — Why ranked here: the hose runs behind the machine where it is crushed when the appliance is pushed into its housing, and a hose without the required high loop lets waste water siphon back into the tub
- An object jammed in the drain pump impeller — Rank: fifth — Why ranked here: glass fragments, olive stones and labels from jars pass the filter when it is not seated correctly and stop the impeller, which produces a hum without flow
- The filter refitted incorrectly after cleaning — Rank: sixth — Why ranked here: a filter that is not locked home lets debris bypass it straight into the pump, so a drainage fault appearing shortly after a cleaning session usually has a simple explanation
- Note: Because the badge is one letter from another and confusing them changes the answer, the order below confirms the machine first, then works the conventional dishwasher chain — water in, wash, heat, drain — in that order, because each stage depends on the one before it.
Check in this order
- The filter assembly in the base of the tub, unscrewed and lifted out — Order: first — Because: it is free, it is designed for owner access, and it is the most likely single finding
- The connection under the sink, the air gap if one is fitted, and the disposer inlet if the machine drains through one — Order: second — Because: the whole thing is outside the appliance and it explains a machine that has never drained properly since the day it was fitted
- The hose behind the machine for kinks and crushing, and whether it rises in a high loop before dropping to the waste — Order: third — Because: it explains both a machine that will not drain and one that fills with dirty water on its own
Owner-safe checks
- Confirm the badge on the data plate matches the badge you searched for. If the plate reads Asko, use the Asko page instead — the platforms differ and so do the parts. Once the plate confirms the machine, work the water path from the fill valve forward. — Step: first — Tools: a torch and a phone camera — Time estimate: a few minutes
- Bail the standing water out into a bowl with a cup and a sponge until the sump is dry enough to work in. Everything below is easier and cleaner once the basin is empty. — Step: second — Tools: a cup, a sponge, a bowl — Time estimate: under a quarter of an hour
- Unscrew and lift out the filter assembly, rinse every part of it under a tap with a brush until the mesh is genuinely clear, and clean the sump beneath it. Refit it so it locks positively home. — Step: third — Tools: a brush, warm water — Time estimate: under a quarter of an hour
- Look under the sink at the waste connection: check the air gap if one is fitted, check the hose is not kinked, and confirm the spigot is not blocked. If a disposer is fitted, run it and check its inlet plug was removed. — Step: fourth — Tools: a torch, a bucket — Time estimate: under a quarter of an hour
- Pull the machine forward far enough to see the drain hose run, check for crushing behind the cabinet, and confirm the hose rises in a high loop before it drops to the waste. — Step: fifth — Tools: a torch — Time estimate: under a quarter of an hour
- Read the data plate on the door edge or the tub rim and check the spelling of the badge against the one you searched. Then run the chain in order — fill, wash, heat, drain — and stop at the first stage that misbehaves rather than at the first part you suspect. — Step: sixth — Tools: a phone camera, a torch — Time estimate: a few minutes
- Stop condition: Stop before removing the drain pump or the sump housing; that means pulling the machine out and working under it with the water and power connected.
Safety
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off. A dishwasher sump can contain broken glass and hot water, and the machine is connected to both mains water and mains electricity under a worktop. Wear gloves when clearing a sump, since broken glass is the most common thing found in a dishwasher filter. Switch the machine off at its isolating switch or breaker before reaching into the sump. Wear gloves when clearing a sump, since broken glass is the most common thing found in a dishwasher filter. Switch the machine off at its isolating switch or breaker before reaching into the sump. unplug-before-service
When to call a technician
The line is anything past the filter, the hose and the waste connection. Call if the pump is silent at the drain step, which points at the pump or its wiring. Call if the filter, hose and waste connection are all clear and water still stands. Call if dirty water appears in the tub after using the sink, which suggests the high loop or the waste arrangement. Call if the machine will not drain and the door has locked with water inside.
Nearest pages of the same kind
What this page does not cover
This page is generalized across every family and model sold under the Asco badge. It does not carry model-specific error-code tables, family-specific service procedures, sealed-system work or parts numbers, and no model-specific page exists beneath it yet — the data plate on your unit is the authority, not this page. For the other faults on this appliance, start from Common Asco Dishwasher Problems (asco-dishwasher-problems) and pick the symptom that matches.
Links: - [Common Asco Dishwasher Problems](/blog/asco-dishwasher-problems) - [Asco Dishwasher: Abnormal Noise or Vibration](/blog/asco-dishwasher-abnormal-noise) - [Asco Dishwasher: Does Not Clean or Dry](/blog/asco-dishwasher-cleaning-performance) - [Asco Dishwasher: Controls, Display or Error Code](/blog/asco-dishwasher-control-fault) - [Asco Dishwasher: Cycle Will Not Run or Complete](/blog/asco-dishwasher-cycle-fault)
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
