The short answer
A Black+Decker AG microwave whose light comes on, whose turntable turns and whose fan runs, but which leaves the food cold, has almost always lost something on the high-voltage side — and that is behind a cabinet no owner opens, because of the capacitor inside. On these models the owner-side list is short and worth doing first: the power level setting, the door closing properly, and on an over-the-range machine the filters. Settle the build before the ranking applies: these models divide on a glass turntable.
What you observe on these models
- The turntable turns and the food stays cold — Controls, fan and light are all fine, which narrows the fault to the part of the oven you may not touch.
- It heats, but far more slowly than it used to — Weak heating rather than none, which usually means the same components on their way out.
- The sound of the machine has changed — Worth noting for the technician, but not something to investigate further at home.
- Settings that were changed and not changed back — A defrost setting heats so gently it reads as no heat at all.
- It has to be pushed to latch — An interlock partially engaged can leave the oven running without heating.
- NEAR MISS — nothing happens at all when you press start — That is a machine that will not start, which is a different page from one that runs without heating.
Causes, ranked for the AG build
- The magnetron or another high-voltage component — It ranks first while also being the one cause an owner may do nothing about. Unplug it and book the visit rather than investigating further.
- The door is not closing fully, or an interlock is partly engaged — Second in the practical order, because a door that needs a push can leave the oven running without the part that heats being enabled.
- Grease-blocked filters or a vent tripping a thermal cut-out — Mid-list and specific to machines mounted over a range, where filters loaded with grease make the oven run hot and cut out.
- A power level, defrost or demo setting — It is placed high purely because it costs ten seconds and it accounts for a real share of no-heat calls.
- The control board or the relay that enables the heat — Last, because it is less common than the magnetron side and equally out of reach.
The order that finds it fastest
- Heat a cup of water and see what happens — A mug of water for a short run tells you whether there is any heating at all, where a plate of food does not.
- Reset the oven to full power and retry — A low level or a defrost programme heats so gently it reads as nothing at all.
- Close the door and feel for a positive latch — A door that needs a push may be leaving an interlock partly engaged.
- On an over-the-range machine, check the grease filters — They wash in hot soapy water and go back damp-dry.
Power off first
Safety
Never open the cabinet of a microwave oven. The high-voltage capacitor inside can hold a lethal charge long after the machine is unplugged, and nothing behind that cover is an owner part on any model. Unplug the oven before cleaning anything, leave every door interlock exactly as it is, and do not run the oven empty.
When to call a technician
The condition here is unusually simple: if it is not a setting, a door or a filter, it is a service call. There is no owner-serviceable path to the parts that heat, on any model, and the value of the checks above is that they are quick and occasionally save the visit entirely.
Other faults covered for the AG models
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
