The short answer
On the Blomberg DWDT dishwashers specifically, this fault sits one level below the brand-generic answer: the models in this family share a layout, and that layout changes which check comes first. The drain path from a dishwasher is short and shared with the kitchen sink, which is why so many of these faults are not in the appliance at all. Listen during the drain step — a humming pump and a silent one point in completely different directions.
What you observe on these models
- The problem started right after the machine was installed — An installation fault rather than a wear fault — the knockout plug is the classic one.
- Debris visible in the standing water — The filter is no longer holding what it catches.
- Water drains very slowly over several minutes — Partial restriction, usually debris rather than a hard blockage.
- NEAR MISS — the dishes are dirty but the tub drains — That is a cleaning fault, not a drainage one.
Causes, most likely first on this family
- Sink waste or air gap restricted — Fourth, and it is confirmed by whether the sink itself drains slowly.
- Drain hose kinked, crushed or wrongly routed — Third, and a missing high loop lets sink water siphon back into the tub, which reads as a failure to drain.
- Disposer knockout plug never removed — Second on likelihood in any kitchen where a disposer has been fitted or replaced recently.
- Where this order differs from the brand-generic page — On this family the access route decides the sequence. The cause that moves up is the one reachable without removing a panel on these models, and the cause that moves down is the one that needs the cabinet opened — so the ranking here is ordered by what this platform lets you confirm first, not only by raw likelihood.
Check in this order, and why
- Check whether the machine has ever drained properly — A machine that has not drained since the day it was installed has a plumbing fault, not a worn part.
- Ask whether the sink drains normally — A slow sink and a dishwasher that will not drain are one fault in the shared waste line, not two faults.
- Lift out the filter and look at the sump below it — Debris, glass fragments and labels collect there, and the drain opening is underneath.
- What this family's layout decides — The construction of these models determines what can be confirmed quickly and what cannot, and the order above follows that directly. It is not a generic checklist reordered; it is the sequence that this platform actually rewards.
Before you open anything
Safety
Switch off at the spur and close the supply valve first. Water and mains wiring are inches apart in this appliance, and a wet hand behind the kickplate of a live machine is the hazard to avoid.
When to call a technician
If everything reachable with the machine isolated is clean and it still misbehaves, that is the call — and a leak of unknown origin under a worktop should be a call the same day rather than the next weekend.
Other faults covered for this family
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Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
