The short answer
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.
