The short answer
On a Thermador dishwasher, water appearing in the sink as it drains most often comes down to a waste disposer knockout plug still in place. Thermador dishwashers are built on the Bosch platform, so there is no heated-dry element and the filter stack is the first check. The first check below needs no tools, and the list stops where a meter on live terminals begins.
What you observe
- Water stands in the bottom at the end of the cycle — The defining symptom, and it is a drain path question.
- The machine hums at the point it should drain — The pump is energised and moving nothing.
- Water backs up into the sink when it drains — The obstruction is outside the machine.
- NEAR MISS — water is on the floor rather than in the tub — That is a leak and a different page.
Causes, most likely first on a Thermador dishwasher
- Waste disposer knockout plug still in place — Ranked first here: a new disposer ships with a sealed inlet, and a dishwasher connected to it can never drain.
- Blocked filter and sump — Ranked second: everything on this machine is caught by a filter rather than ground up, so a neglected filter starves the drain pump directly.
- Kinked or blocked drain hose — Last on this list: the hose is flexible, it is behind the machine, and it is crushed every time the cabinet is pushed back.
Check in this order, and why
- Ask whether a disposer was fitted just before the fault started — Timing alone usually settles this one. First: likeliest cause, least effort.
- Twist out the filter stack and clear the sump beneath — Glass chips and labels collect exactly there. Second: it separates the next two causes.
- Look behind the machine at the hose route — Any sharp fold is the fault. Third: only once the checks above are clean.
What an owner can safely check
- Check whether a disposer or sink was replaced recently — A sealed inlet plug is the commonest cause of a never-drained machine.
Tools: noneAbout 5 min
- Bail the standing water out with a jug and a sponge — You cannot inspect a sump underwater.
Tools: jug, spongeAbout 15 min
- Remove the filter stack and clear the sump recess by hand — Wear a glove: broken glass ends up here.
Tools: glovesAbout 15 min
- Ease the machine forward and inspect the hose for kinks — Do not pull it out fully: the supply line is short.
Tools: torchAbout 15 min
- STOP HERE if the next step needs a meter on live terminals — That is where an owner check ends and a service call begins.
Before you open anything
Safety
Unplug the appliance or switch off its breaker before removing any panel. A capacitor can hold a charge after the power is off.
When to call a technician
Call once the filter, the spray arms and the drain path are all proven clear and the fault is unchanged, because the next tests are on live terminals inside a wet cabinet. Call immediately if you see water at the electrical panel, if the cabinet trips the breaker, or if there is standing water under the machine rather than in it.
Nearest pages of this class
What this page does not cover
This page covers Thermador dishwashers as a class, not one family or model line. It reasons from how Thermador builds this appliance — enough to rank the causes, not enough for wiring colours, torque figures or part numbers, which differ by family. Where a model-specific page exists it is linked here and is the better answer; this class page has no such child yet, so nothing is withheld by omission.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
