The short answer
A Black+Decker microwave showing this usually tells you one thing: an oven that runs without heating has almost always failed at the door or at the test, not at the magnetron. The water test, the power level and the door latch are free and settle most of these. Past them, the case stays closed and it becomes a replacement decision.
What you actually see
- The oven runs a full cycle and the food is cold — Turntable turning, light on, fan running, nothing warm — the classic no-heat picture.
- Food heats but takes far longer than it used to — Partial heating is a different fault from no heating and has a different cause list.
- Heat stops part way through a long cycle — Stopping mid-cycle points at a thermal device rather than at a permanent failure.
Causes, ranked for this microwave
- Door latch not fully closing its switches — The usual answer. a microwave will not produce heat unless every door switch confirms the door is shut, and a worn latch closes some of them and not others. Rule it in or out properly here; a maybe at this position costs an hour further down.
- Testing with too small a load — The runner-up. it belongs high because it costs nothing to rule out and because a bad test is the reason for a fair number of these calls. Getting a definite answer here is worth more than a quick look at the three below it.
- Power level set low or a mode left engaged — Third. a low power setting is a duty cycle, so the oven runs the full time and heats for a fraction of it — which feels like weak heating. If this is the answer, the rest of the list stops mattering entirely.
What to check, in order
- First — the door latch and how it closes — Look at the latch hooks and the striker for wear or a chipped edge. Both are visible with the door open.
- Second — how the oven was tested — Heat a cup of water for a short period and feel the cup and the water. That is the standard test and it removes all ambiguity.
Checks an owner can do safely
- Step 1. Let it cool and retry — Unplug the oven and leave it for an hour, then repeat the water test. Heat that returns after cooling points at a thermal cut-out and at airflow.
Tools: noneAbout 60 min
- Step 2. Inspect the latch and striker — With the door open, look at the latch hooks and the striker they engage for wear, chips or a missing piece.
Tools: flashlightAbout 5 min
- Step 3. Run the cup-of-water test — Put a mug of cold water in the centre of the turntable and run a short cycle at full power. Feel the water afterwards. This removes every ambiguity about whether the oven heats.
Tools: mug, waterAbout 5 min
Before you open anything
Safety
Unplug it, and treat the inside as off limits. The high-voltage section of a microwave remains dangerous with the power disconnected. A damaged door, a bent latch or a failed switch is a reason to stop using the oven, never a reason to work around it.
When this becomes a service call
Stop and call when the next thing to do meets any of these. The case stays closed regardless of the fault. A microwave stores a dangerous charge after it is unplugged, and there is no owner-serviceable part behind that case.
Sources
General guidance- The Control of Hazardous Energy (Lockout/Tagout) — OSHA 1910.147 and manufacturer service manuals, fetched
Nearest pages
What this page does not cover
Treat what follows as the class-level answer for a Black+Decker microwave. It will not tell you which board your unit has, which part number fits it, or what a particular code means on a particular family, because those differ within the range. The family and model pages beneath this one carry that, and they are linked under Related pages.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
