The short answer for B models
When an Avanti B microwave runs without heating, the first thing to establish is that it really is not heating. A cup of water for a minute is a far better test than a plate of food, which can be cold in the middle and hot at the edge for reasons that have nothing to do with a fault.
What it looks like from the outside
- The oven runs, the light is on and the plate turns, but food stays cold — The defining symptom, and it rules out the control and the motor immediately.
- A loud buzz or hum while it runs cold — The transformer is energised and something downstream of it is not working.
- The oven cuts out partway and then runs cold — A thermal protector operating, often because the cooling fan or the vents are blocked.
- No sound at all beyond the fan — A transformer that is not being energised, which changes the likely cause.
- NEAR MISS — the food is hot at the edge and cold in the middle — That is usually the food and the method rather than the oven.
What actually fails on these models, in order
- Magnetron at the end of its life — Ranked first because it is the part that makes the energy and the one that wears out, and gradual loss of power is its signature.
- Vents blocked by the installation — On a built-in or over-range oven, a blocked vent path is an owner-fixable version of the same fault.
- High-voltage transformer failed — Less common than the diode and the capacitor it feeds, and the symptom is the same.
- Door interlock inhibiting power — One switch of the three can stop the power while letting the light, the fan and the plate run normally.
The order that saves the most time
- Before anything else — This order exists because the cheap causes are also the likely ones: one of the four named above can be settled on B models before a tool comes out.
- Listen to what the oven does while it runs — A heavy buzz means the transformer is energised.
- Check the power level and the programme selected — A defrost programme or a low power level explains a cold result with nothing wrong at all.
- Put a cup of water in and run it for one minute — Warm water means the oven works and the problem was the food.
- Stop once you have the symptom described and leave it unplugged — Everything below this line is behind the case, and the case must not come off.
Before you do anything else, unplug it
Safety
Unplug the microwave at the socket before you examine anything, and keep the case closed. The capacitor in the high-voltage section can hold a lethal charge after the power is off. Do not run the oven empty, do not defeat any door interlock, and take the appliance out of service entirely if the door is damaged or the oven runs with the door ajar — the door is what contains the energy.
Models in the B family
Reference| Model number | Family key |
|---|---|
| B20PXP78 | avanti:microwave:b |
When to call a technician
Call for anything that is not cleaning. The high-voltage capacitor inside can hold a lethal charge after the oven is unplugged, so there is no owner repair on this appliance beyond the cavity, the turntable and the door seal face.
Other B problems we cover
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