The short answer
A microwave that will not start is either not being allowed to start or is not receiving power, and the display tells you which in a second. A lit display with a dead start button is a permission problem, almost always the door. Look at the display. Lit means power is present and something is withholding permission; dark means the supply, the internal fuse or the control has failed. On a Smeg microwave the cause that ranks first is control lock or child lock engaged.
What you observe
- The machine beeps at a press but does not run — The keypad works, so the door or the lock is the candidate.
- A lock or key symbol is showing on the display — The control is refusing input deliberately.
- NEAR MISS — the machine runs but the food stays cold — That is a heating fault and it has its own page.
Causes, most likely first on a Smeg microwave
- Control lock or child lock engaged — A lock symbol swallows every key press and gives no other warning, and on many machines it is set by a long press that is easy to trigger by accident. It ranks first on a Smeg microwave because the European control aborts rather than pushing through a fault, so the sensor and lock causes surface ahead of the mechanical ones.
- Door not latching, so the interlocks never make — The machine is designed not to energise until every interlock confirms the door in the right order, and a worn hook or a dropped hinge breaks that sequence. Second on this platform: the interlock chain is the machine's primary safety system and it holds the machine still the moment anything in it is wrong.
- Touch panel or membrane failed — One key stops responding while others work, which is a membrane fault rather than a control fault, and it is common on panels that get wiped constantly. Ranked here because a dead key beside working keys is unambiguous and points at the panel, not the board.
- No power at the socket, or a tripped breaker — A dark display with a live machine behind it is impossible, so a dark display sends you upstream to the socket and the breaker first. Last, and the reason to work down the list rather than guess: a dark display means the fault is upstream, and upstream is free to check.
Check in this order, and why
- Look for a lock symbol on the display and hold the marked key — Most machines clear a lock with one long press.
- Open the door and shut it deliberately, listening for the switch clicks — Several distinct clicks are normal; one soft click is not.
- Press every key in turn and note which produce a beep — A single dead key is a membrane; a whole dead panel is not.
What an owner can safely check
- Hold the key marked with a lock or a key symbol until the display clears — Check the manual for the exact key if nothing is marked.
About 5 min
- Close the door firmly and squarely, then press start again — Clean the latch hooks and door face if the close feels loose.
Tools: clothAbout 5 min
- STOP at the point where the next check means live terminals or a panel removed — Everything past that line is a technician's work, however likely the cause above it looks.
Before you open anything
Safety
Never open the case of a microwave — the high-voltage capacitor can hold a lethal charge long after it is unplugged — and never hold, tape or wedge the door to force the machine to run.
When to call a technician
Call, or price a replacement, once the socket is proven live, the door latches cleanly and no lock is showing: everything left is inside the case. On a European-controlled machine, ask what the control was reporting when it stopped — it usually records why it aborted, and that shortens the visit.
Nearest pages of this class
What this page does not cover
What this page covers is the microwave class as Smeg builds it, not an individual family or model line. If a page exists for your particular family or model, it is linked above and it is the better answer — go there first when your model is named. Left out on purpose: part numbers, connector colours, disassembly order and torque values, because every one of those varies by family.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
