Door-latch, water-supply and control-lock issues dominate first checks.
Start Here
Check control lock and delay.
Close latch firmly.
Verify breaker and outlet.
Confirm water valve is open.
Look for standing water from a prior failed drain.
Appliances rarely fail in a way that names the defective component for you. Door-latch, water-supply and control-lock issues dominate first checks. For dishwasher will not start, 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: check control lock and delay, then close latch firmly. 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 verify breaker and outlet. Then decide whether confirm water valve is open 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 forcing a damaged latch, resetting without noting error lights, and opening live panels. 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 check control lock and delay.
Remove external causes first; specifically verify close latch firmly.
With power isolated where required, inspect verify breaker and outlet and then evaluate confirm water valve is open 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
Forcing a damaged latch.
Resetting without noting error lights.
Opening live panels.
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.