The short answer
On Blomberg DW dishwashers this symptom narrows faster than it does at brand level, because the construction of this family rules some causes in and others out early. Before suspecting the pump, check the one connection almost every installation gets wrong — the disposer knockout plug. Listen during the drain step — a humming pump and a silent one point in completely different directions.
What you observe on these models
- Dirty water appears in the sink when the dishwasher drains — The shared waste line is restricted rather than the machine.
- 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.
- NEAR MISS — water is on the floor rather than in the tub — That is a leak and it has its own page.
Causes, most likely first on this family
- Sink waste or air gap restricted — Fourth, because an air gap fitting on the worktop blocks with debris and is easily missed.
- 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.
- How this ranking departs from the brand-level article — The brand-generic page ranks purely by frequency. On this platform the component that sits behind the most accessible panel moves up, because confirming it is quick and confirming the others is not — that changes the practical order even where the underlying frequencies are similar.
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
Turn the power off at the isolating switch and close the valve under the sink before touching a fitting. Let a hot cycle cool before reaching into the tub — the heating element and the water are both hot at the end of a programme.
When to call a technician
Stop where the machine has to come out. Unfastening a built-in dishwasher means handling a pressurised supply, a waste connection and a mains circuit in a confined space, and that is a technician's job rather than an owner check.
Other faults covered for this family
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
