Thermador Dishwasher Not Draining — i30 Error Code & Drain Pump Fix (DWHD770WFM, DWHD870WFP, DWHD650WFP)

Common Symptoms

• Standing water at the bottom of the dishwasher tub after cycle ends
• i30 error code on the Thermador display panel (AquaStop/flood protection triggered)
• i20 error code (drain pump blocked or slow drainage)
• Dishwasher stops mid-cycle and refuses to restart
• Gurgling or straining sounds from drain area during or after wash cycle
• Water pooling on floor near the dishwasher base

Most Likely Causes

1. 1

   Clogged Filter Assembly (Most Common — Free Fix)

   Thermador dishwashers use the same BSH two-part filter system as Bosch: a cylindrical fine-mesh microfilter (quarter-turn removal) sits inside a flat coarse pre-filter at the base of the tub. Food particles, grease, and mineral deposits accumulate here and restrict drain flow — even partial clogging can trigger i20 as the drain pump cannot move water fast enough. Thermador recommends cleaning the filter monthly, but most owners never do it. Cleaning the filter resolves drain failures in approximately 50–60% of Thermador dishwasher no-drain service calls.

2. 2

   AquaStop Anti-Flood Device Triggered (i30 Error)

   The i30 error code means the AquaStop float sensor in the base pan has risen — detecting water in the pan and cutting off the water supply inlet. On Thermador dishwashers, this is most often caused by condensation accumulation in the insulated base pan over time (same mechanism as Bosch E15). The fix: tilt the dishwasher forward at 45 degrees to drain the base pan water, allow the float to settle, restore power, and run a test cycle. If i30 returns after a few cycles, there is an active slow leak — inspect the door gasket, drain hose connection, and spray arm hub O-ring.

3. 3

   Kinked or Improperly Routed Drain Hose

   The drain hose on Thermador dishwashers runs from the drain pump at the base of the tub through the sink cabinet to the drain connection. A kinked hose — often caused by pushing the dishwasher back into its bay after installation — blocks water flow and triggers i20. The drain hose must also maintain a high loop (routed up to the underside of the counter at least 20 inches above the floor) to prevent siphoning. Thermador's BSH service guide specifies a minimum 20-inch high-loop height.

4. 4

   Garbage Disposal Knockout Plug Not Removed

   If the Thermador dishwasher drain hose connects to a new garbage disposal, the knockout plug inside the disposal inlet port must be punched out during installation. A disposal with the knockout intact completely blocks drainage. This is a very common new-installation cause of i20 — and the fix is free: insert a screwdriver into the disposal drain inlet and tap out the knockout plug with a hammer.

5. 5

   Drain Pump Failure or Blocked Impeller

   The drain pump motor on Thermador dishwashers is a small permanent-magnet motor with a plastic impeller. Hard debris (broken glass, bone fragments, pits from olives) can jam the impeller and prevent the pump from turning. A jammed impeller often triggers a blown thermal protector inside the pump motor. Test the pump motor resistance: disconnect power, remove the pump from the sump base, and probe the pump terminals — a healthy Thermador drain pump reads approximately 10–30Ω. OL = failed motor, replace. A jammed (but not burned) pump motor may sometimes be cleared by removing the debris and testing continuity again.

6. 6

   Door Gasket Leak Causing i30 Recurrence

   If the i30 AquaStop error returns repeatedly after the tilt procedure, a door gasket leak is the most common source. The door gasket on DWHD770WFM and DWHD870WFP models can pull away from the bottom corners of the door frame — a gap as small as 1–2mm allows steam and water to drip into the base pan over multiple cycles. Inspect the gasket bottom corners closely: look for deformation, pulling, cracks, or hardening. Replacement gasket: $20–$45, model-specific.

Quick DIY Checks

1. 1SAFETY FIRST — Switch off the Thermador dishwasher circuit breaker or unplug the unit before any internal inspection. The i30 AquaStop code means water is in the base pan near electrical components — do not operate the machine until the base pan is drained and the source is identified.
2. 2CLEAN THE FILTER ASSEMBLY — Open the dishwasher door. Turn and lift out the cylindrical microfilter (quarter-turn counterclockwise on DWHD770WFM and DWHD650WFP), then lift out the flat coarse pre-filter beneath it. Rinse both filters under hot running water and scrub with a soft brush to remove grease and food debris. Reinstall both filters firmly (the cylindrical filter must snap and lock — verify it cannot be pulled straight up without rotating). Run a drain-only cycle: select a 'Quick Wash' or run the machine and press CANCEL during the wash phase — the dishwasher will pump out residual water.
3. 3i30 — TILT AND DRAIN THE BASE PAN — Place thick towels on the floor in front of the dishwasher. Disconnect power. Open the door slightly (2–3 inches) and grip the sides of the dishwasher near the base. Tilt the unit forward to approximately 45 degrees and hold for 30 seconds — water in the base pan will drain through the front bottom gap onto your towels. Return to upright. On DWHD770WFM models, remove the lower kickplate panel (two screws) first to access the drain path clearly. Plug in, restore power, and run a short rinse cycle — i30 should clear automatically.

Repair vs Replace

Recommended Tools & Parts

• Thermador Dishwasher Drain Pump Assembly

  Replacement drain pump motor for Thermador BSH-platform dishwashers (DWHD770WFM, DWHD870WFP, DWHD650WFP, DWHD660WFM). Fixes i20 drain fault when pump motor tests OL or impeller is damaged. Healthy resistance: 10–30Ω. BSH/Thermador part 00647878 or equivalent.

  $50–$80

  Buy on Amazon →

• Thermador Dishwasher Door Gasket / Door Seal

  Replacement perimeter door gasket for Thermador StarDish and Star Sapphire dishwashers. Fixes recurring i30 errors caused by base pan condensation from door seal gaps — especially at bottom corners. Model-specific; verify by full model number.

  $20–$45

  Buy on Amazon →

• Thermador Dishwasher Drain Hose

  Replacement corrugated drain hose for Thermador dishwashers — resolves drain failures from cracked, kinked, or deteriorated hose. Measure existing hose length and confirm connection diameter (Thermador uses 22mm / 7/8 inch OD drain hose on most BSH models).

  $15–$30

  Buy on Amazon →

• Thermador Dishwasher Filter Assembly

  Replacement two-part filter set (cylindrical microfilter + flat coarse pre-filter) for Thermador dishwashers. Replace if filter is torn, has structural cracks, or cannot be cleaned. Thermador recommends annual filter replacement in hard-water areas.

  $20–$40

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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