The short answer
A completely dead mounted unit is usually a supply problem, and the plug in the cabinet above is the leading suspect. A unit that lights up but refuses to run is nearly always the door chain or an active lock, in that order.
Which of these is yours
- No display, no light, no fan — Supply. Start above the unit, not inside it.
- Display lit, start key beeps and cancels — A refusal, not a power failure.
- A lock legend showing on the panel — The control is doing what it was told.
- Display lit but keys in one area do nothing — That is the controls page rather than this one.
- The breaker is tripped in the panel — Investigate before resetting more than once.
- Not this fault: it runs but the food stays cold — Go to the not-heating page.
Ranked for a mounted unit
- Plug unseated in the cabinet socket above the unit — First and most often, precisely because nobody can see it.
- Breaker tripped or a shared circuit overloaded — Second, and worth checking before any tool comes out.
- Door not satisfying the interlock chain — Third, and the leading cause when the display is alive.
- Child lock or demo mode active — Fourth: free to clear and easy to set by accident.
- Keypad or control board failure — Fifth, and usually visible as dead keys or missing segments.
- Internal fuse open after a fault — Last, and it is service work because it means something else failed first.
The order that saves a call-out
- Open the cabinet above and push the plug fully home — Leading cause, zero cost.
- Check the breaker panel for a tripped device — Second cheapest check available.
- Close the door firmly and listen for the latch — Answers the refusal branch immediately.
- Look for a lock legend on the panel and clear it — Last of the free checks and a common finding.
Owner checks
- Reseat the plug in the cabinet socket above the appliance — Use a step, not a chair, and switch the breaker off first.
About 15 min
- Test that socket with a lamp or a phone charger — Proves or clears the supply in one move.
Tools: lampAbout 10 min
- Reset a tripped breaker once only — A breaker that trips again is reporting a fault, not misbehaving.
About 10 min
- Open the door fully, close it firmly, and press start — The interlock chain needs a properly seated door.
About 5 min
- Hold the lock key for the period printed beside it — Clears the most common false failure on any microwave panel.
About 5 min
- Stop before the case is opened for any reason — The stored charge inside can be lethal even when unplugged.
Before reaching above the range
Safety
Switch off the breaker before reaching into the cabinet above a mounted microwave, and use proper steps rather than the cooktop. Unplug the appliance or switch off its breaker before removing any panel; a capacitor can hold a charge after the power is off. Leave the door latch and its switches exactly as built, and never wedge or hold a door to make a unit run.
When to call
Call when the socket is proven good and the unit is still dead, because the next candidate is an internal fuse that only opens when something else has failed. Call as well when a properly latched door still produces a refusal, when keys or display segments are dead, and immediately if the breaker trips each time the unit is connected. A mounted unit is heavy and awkward to remove, which is another reason not to attempt access from a step ladder.
Other pages here
Scope of this page
Generalized across families, written for mounted installations; the companion page covers counter-standing units. Where a family-specific or model-specific page exists it is the narrower answer. Not here: fuse ratings, mounting-plate hardware, interlock switch part numbers and any procedure that involves lowering the appliance from its bracket.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
