Thermador dishwasher leaving water in the tub

An inch of grey water in the bottom of the tub is the single most common dishwasher complaint, and it is usually not the dishwasher. The drain path runs from the sump, through a pump, up a hose, and into either a disposer or a waste tee under the sink. Any of those can be the blockage, and three of the four sit outside the appliance.

Work the path from the inside out

Start at the filter. Twist out the cylindrical filter in the floor of the tub and lift the flat screen underneath it. Grease sets into that mesh as a continuous film, and a film you can barely see is enough to halve the flow. Wash both under hot water with a brush. If the tub drains after that, you have found it — and you have found the maintenance interval you should be keeping.

Next, look in the sump with a torch. Fragments of glass, olive stones, and the paper labels off jars all end up there, and any of them can wedge in the pump impeller. A pump that hums without moving water is describing an obstruction as clearly as it can.

Then everything under the sink

If the appliance was installed or replaced recently, check the disposer. A new disposer ships with a knockout plug sealing the dishwasher inlet, and it has to be driven out before the drain hose is connected. When that step is missed, the dishwasher runs a full cycle and pumps against a solid wall of plastic. The symptom is a tub that never drains at all from day one. This turns up regularly in Oakleaf Plantation kitchens where the disposer and the dishwasher have been changed at different times by different trades.

Then check the high loop. The drain hose must rise close to the underside of the counter before it drops to the disposer or the waste tee. Without that loop, sink water siphons back into the tub, and the owner’s description is usually “it drains, but there is dirty water in it the next morning”. That is a different fault from a blocked drain and it is fixed with a hose clip.

If the sink deck has an air gap — the small chrome cylinder beside the tap — lift the cover and clean the chamber. They pack solid with the same grease and solids as the filter, and when they do, water backs up onto the deck as well as staying in the tub.

What is not the cause here

Cleaning products are not the answer to a drain fault. A cleaner or a rinse additive poured into a tub that will not empty circulates for a cycle and leaves the same water behind, and it costs an evening that would have been better spent under the sink with a torch.

Detergent quantity is worth a look for a different reason. Overdosing produces a foam layer, and foam slows drainage measurably as well as leaving residue on the tub floor and film on glassware. If the machine drains slowly rather than not at all, and the glasses have been cloudy for a while, halve the dose for a week before assuming a component has failed.

The other thing that is not the cause is the appliance being old. These machines do not develop drain faults from age; they develop them from a blocked path, and three quarters of that path sits outside the machine.

When it is the pump

If the filter is clean, the sump is clear, the disposer is open and the high loop is correct, the drain pump or the circuit driving it is the remaining candidate. That is diagnosed by watching what the pump does when the drain phase starts: nothing at all, a hum with no flow, or a normal run that still leaves water behind all point in different directions.

The flat $129 diagnostic covers making that determination properly, with a written estimate before any work begins and the fee credited toward the repair. Genuine OEM parts, 90 days on labor, 365 days on parts.

Stop using the machine and book if water is escaping onto the floor, if the cabinet base is damp, or if the appliance trips a breaker mid-cycle. Standing water in the tub on its own can wait for a scheduled appointment.