The short answer
A Thermador dishwasher often detects its own leak before you do: the base-pan protection senses water in the tray, shuts the programme down and runs the drain pump, which owners report as a machine that hums and will not start. Where water does reach the floor of a built-in installation, the drain and supply connections rank above any component.
Causes, ranked for this Thermador dishwasher
- Base-pan protection latched by a detected leak — Why: It ranks first because it changes the whole response: the machine has already found water in its tray and stopped, so this is a leak hunt rather than a start fault.
- Drain hose high loop lost or clamp loose — Why: On a built-in the hose is routed behind cabinetry, and a loop that was never formed lets sink water siphon back and overflow — dirty water is the tell.
- Supply connection at the inlet — Why: Made at installation and then concealed, so a fitting never fully tightened weeps into the cabinet base for months before anything is visible.
- Door seal displaced or held off by a load — Why: A tall item in the lower rack holds the door off its seal at one corner, producing a localised drip that reads as a gasket failure.
- Sump or pump seal — Why: The classic tub leak and a real one, but ranked below the installation causes because a built-in conceals installation defects and exposes component ones.
What to check, in order
- listen for a continuous pump hum with no fill. — Because: that is the base-pan protection, and it turns the diagnosis from a leak search into a confirmed leak.
- dry everything and identify the phase in which water first appears. — Because: phase eliminates most of the list before any panel is removed.
- check the drain hose in the adjacent cabinet for a high loop and a tight clamp. — Because: it is the commonest installation defect on a built-in and it is visible without moving the machine.
- look for staining or swelling at the cabinet base under the supply connection. — Because: a fill-phase leak leaves a history there clearer than the leak itself.
Checks you can safely do yourself
- Switch off power at the breaker and close the supply stop before doing more than looking. — Tools: none — Time: a few minutes
- Listen at the machine for a continuous low pump hum without any fill, which indicates the base-pan protection has operated. — Tools: none — Time: a few minutes
- Dry the floor, toe kick and neighbouring cabinet base, then lay paper towel at each and run a short programme if the machine will start. — Tools: paper towel — Time: the better part of an hour, mostly waiting
- Trace the drain hose in the adjacent cabinet, confirm it rises above the tub before dropping and tighten its clamp. — Tools: a torch and a nut driver — Time: several minutes
- Inspect the cabinet base under the supply connection for staining or swollen board. Stop here: the base pan and sump need the machine drawn out of a finished opening. — Tools: a torch — Time: several minutes
Before you open anything
Safety
unplug-before-service
If the machine is pumping continuously without filling, treat it as a leak that has already been detected and stop using it until the base is checked. Kill power at the breaker rather than the door latch before reaching under the machine, and close the supply stop before touching a fitting. A soft cabinet base means the damage is already under way.
Where the owner fix ends
Correcting a drain loop, tightening a clamp and tracing the leak phase are owner work. Call a technician immediately when the base-pan protection has latched, because water has reached the base of a machine built into cabinetry; and call when the leak arrives from beneath the tub, since removing a built-in from a finished opening is not an owner job.
Nearest pages of the same kind
Generalized information — what this page does not cover
family model
This page is generalized information about Thermador dishwashers and does not separate the fully integrated, panel-ready and stainless families, whose access panels and hose routing differ. Because these machines go into custom cabinetry, the installation causes weigh more heavily here than on a freestanding machine. No family-level or model-level page exists in this reference yet; when one is published it will be linked here.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
