The drain path extends beyond the dishwasher itself.
Start Here
Clean filter and sump area.
Inspect drain hose.
Check sink disposal connection.
Verify high loop/air gap arrangement.
Listen for drain pump.
Most unnecessary repairs begin with a real symptom and an unsupported conclusion. The drain path extends beyond the dishwasher itself. For dishwasher will not drain, concentrate on fill, circulation, filtration and drain flow. Use every working function as evidence: if one stage still behaves normally, that fact eliminates causes that would have stopped the appliance earlier in the sequence.
Observe the timing before touching anything. Note what happens immediately after Start, what changes just before the fault, and what remains normal afterward. Lights, relay clicks, water movement, motor or fan sounds, heat, vibration and error codes are useful only when tied to a point in the cycle. A fault that appears instantly is a different problem from one that appears only after the machine warms up or reaches a later stage.
Begin with the cheapest conditions to verify: clean filter and sump area, then inspect drain hose. Do not merely glance at them. Compare the actual condition with the manual, correct anything obviously wrong, and retest before moving deeper. Simple installation, maintenance and user-setting problems regularly imitate failed electrical parts.
If those checks pass, move to check sink disposal connection. Then decide whether verify high loop/air gap arrangement can be evaluated safely with power isolated. Choose one test that answers one question: blocked or clear, open or closed, free or jammed, intact or electrically open. If a test result would not change your next decision, the test is probably not worth doing.
Avoid putting fingers in a pump with power connected, using harsh drain chemicals in the appliance, and overlooking a blocked sink connection. All three skip evidence and can turn a minor fault into an expensive one. After a correction, reassemble guards and connectors, restore normal settings, and reproduce the original operating conditions. A single successful start is not proof; the original symptom must stay gone through the stage that used to fail.
A Safe Step-by-Step Check
Document the exact symptom and pay special attention to clean filter and sump area.
Remove external causes first; specifically verify inspect drain hose.
With power isolated where required, inspect check sink disposal connection and then evaluate verify high loop/air gap arrangement only if it can be done safely.
Reassemble fully and run a controlled test under the conditions that previously caused the fault.
Common Beginner Mistakes
Putting fingers in a pump with power connected.
Using harsh drain chemicals in the appliance.
Overlooking a blocked sink connection.
STOP AND GET HELP: If the next useful test requires exposed live mains, defeating a safety interlock, opening a sealed refrigeration circuit, disturbing gas controls, or entering a microwave high-voltage section, the diagnosis has reached the professional-service boundary.