Question 1

the sensor cook functions keep overcooking my popcorn or melting my butter.

Accepted Answer

DIAGNOSIS The humidity sensor is being triggered incorrectly, often because you're using the wrong container or the room is too humid. FIX For popcorn, always use a microwave popcorn bag designed for sensor cooking. Place it centered on the flatbed. For 'Melt Butter', use a small, uncovered ceramic or glass dish with the butter in a single layer. IF THAT DIDN'T WORK Wipe the interior dry before using sensor cook. Ambient steam or moisture from a previous cook can fool the sensor. Also, never cover the dish with plastic wrap during a sensor function—it traps steam and causes overcooking. HEADS UP Sensor cooking is an estimate. Start with the minimum time suggested for your food and stop it manually if you hear popping slowing down (for popcorn) or see the butter is melted.

Question 2

food heats unevenly in this microwave, some parts are boiling and others are cold.

Accepted Answer

DIAGNOSIS The Breville Smooth Wave BMO850BSS is designed as a "turntable-free" microwave. Unlike traditional units that rotate the food through a stationary beam of microwaves, this model uses a series of internal antennas and a specialized waveguide to bounce microwaves throughout the cavity. This creates a "stirrer" effect intended to distribute energy evenly. However, when food heats unevenly—where some areas are boiling and others remain frozen or cold—it is typically because the standing wave patterns are creating localized "hot spots" and "cold spots" (nodes) that the internal antenna system cannot fully neutralize for the specific density of your food. This happens most frequently with dense, high-moisture foods (like stews, pasta, or thick cuts of meat) where the outer layers absorb the majority of the microwave energy, shielding the center. Because there is no physical rotation to move the food through different wave phases, the energy remains concentrated in specific geometric coordinates. You can confirm this by placing a thin layer of shredded cheese on a flat plate and heating it for 30 seconds; if the cheese melts in distinct patches while other areas remain solid, the wave distribution is functioning as designed, but your food placement is the issue. FIX To overcome the lack of a turntable and eliminate cold spots, you must manually manage the energy distribution and food geometry. Follow these precise steps: Utilize the "Ring" Arrangement: Never place food in a dense pile in the center of the microwave. Instead, arrange items in a circular pattern around the perimeter of the glass tray, leaving the center of the plate empty. This places the food directly in the path of the most active wave reflections. Select the Correct Power Level: Avoid using the default "High" setting for items taking longer than 3 minutes. Press the 'Power' button and use the dial to drop the power to Medium (50%) or Medium-Low (30%). This allows the energy to penetrate the core of the food without overheating the exterior. Implement the "Halfway Pivot": Set a timer for half the total cooking time. When it beeps, open the door and physically rotate the dish 180 degrees. If you are heating a liquid, stir it vigorously from the outside in toward the center. Use Shallow, Wide Glassware: Swap deep bowls for wide, shallow Pyrex or ceramic dishes. Increasing the surface area reduces the distance the microwaves must travel to reach the center of the food mass. Apply a Moisture Barrier: Cover the dish with a microwave-safe lid or damp paper towel. This traps steam, which conducts heat into the "cold spots" via convection, supplementing the microwave energy. IF THAT DIDN'T WORK Check for Wave-Blocking Containers: Ensure you are not using "microwave-safe" plastic that is excessively thick or contains metallic decorative rims. Even a thin gold or silver rim on a plate will reflect microwaves away from the food, creating a massive cold spot on one side of the dish. Switch to plain borosilicate glass. Verify Cavity Cleanliness: Inspect the waveguide cover (the small rectangular panel on the right interior wall). If there is a buildup of grease, splatters, or burnt food residue, the microwaves will reflect off the grease rather than passing into the cavity, leading to erratic heating patterns. Clean it with a mixture of mild soap and water. Test with a "Water Load": Fill a large glass bowl with water and heat it for 2 minutes. If the water is boiling uniformly, the microwave's magnetron and antenna are functioning correctly, and the issue is solely with the density and placement of your specific food items. Reset the Control Board: In rare cases, a glitch in the power-level logic can occur. Unplug the BMO850BSS from the wall outlet for exactly 60 seconds to discharge the capacitors, then plug it back in to reset the internal timing and power sequences. HEADS UP Avoid Overloading: Do not crowd the cavity with multiple containers; this disrupts the wave bounce and creates significant cold zones between the dishes. Avoid Metal Foil: Never use aluminum foil to "trap heat" in this model; the antenna system is highly sensitive to metal, which can cause arcing or permanent damage to the waveguide. Mind the Center: Remember that the center of the Smooth Wave cavity is generally the lowest energy zone; always prioritize the edges of the tray for the densest parts of your meal. Clean Regularly: Because this unit relies on wave reflection, a dirty interior wall can actually change the heating pattern of the machine.

Question 3

the clock on my breville microwave resets to 0:00 every time i unplug it, is the battery dead?

Accepted Answer

DIAGNOSIS The Breville Smooth Wave BMO850BSS is designed with a volatile memory system for its clock function. Unlike a traditional wall clock or some high-end ovens, this microwave does not utilize a long-term CMOS battery or a replaceable coin cell to maintain the time during a power disconnect. Instead, it relies on a capacitor-based backup system that can only hold the clock memory for a very short window—typically less than 30 seconds. When you unplug the unit, the capacitor drains almost instantly. Because there is no permanent battery backup integrated into the control board, the microprocessor loses its volatile memory and reverts to the default "0:00" state. If you are seeing this happen even during a momentary flicker of power, it indicates that the capacitor on the control board has degraded or that the unit is simply performing as designed by clearing its cache upon loss of AC current. You can confirm this by plugging the unit in, setting the time, and then unplugging it for just 10 seconds; if it resets, it is the standard behavior of the BMO850BSS circuitry. FIX Since there is no user-serviceable battery to replace, the "fix" involves ensuring a stable power connection to prevent unnecessary resets and properly re-initializing the clock using the specific sequence required for the Smooth Wave interface. Ensure the power cord is seated firmly in a grounded 120V outlet. Avoid using extension cords or power strips, as voltage drops can sometimes trigger a logic reset on the control board. Press the Clock button on the control panel. The display will begin to flash. Use the Dial (the rotating knob) to adjust the hours and minutes. Rotate clockwise to increase the time and counter-clockwise to decrease it. Press the Clock button again or the Start button to lock in the time. If the clock continues to drift or reset while plugged in, perform a hard logic reset by unplugging the unit for exactly 60 seconds and then plugging it back in to clear any static charge from the capacitors. IF THAT DIDN'T WORK If the clock resets while the microwave remains plugged in, or if it refuses to hold the time for more than a few hours, you are dealing with a hardware failure rather than a lack of a battery. Control Board Capacitor Failure: The electrolytic capacitors on the main PCB (Printed Circuit Board) may have leaked or bulged. This prevents the board from holding the minimal charge needed to maintain the clock cycle. This requires a professional replacement of the control board assembly. Intermittent Power Supply: Check for a loose connection at the wall outlet. If the prongs on the microwave plug are slightly bent or the outlet is "loose," the unit may be experiencing micro-interruptions in power that trigger the 0:00 reset. Try a different circuit in your kitchen to isolate the issue. Firmware Glitch: In rare cases, the internal logic hangs. Unplug the unit and hold the Start button down for 15 seconds while unplugged to discharge any remaining energy from the board, then plug it back in. Voltage Fluctuations: If you live in an area with "brownouts" or unstable grids, the BMO850BSS may reset. Installing a small UPS (Uninterruptible Power Supply) or a high-quality surge protector can stabilize the current and prevent the clock from resetting during voltage dips. HEADS UP Never attempt to open the chassis of the BMO850BSS to search for a battery. Microwaves contain high-voltage capacitors that can hold a lethal electrical charge even when the unit is unplugged. Avoid using "Eco Mode" or power-saving strips that automatically cut power to the appliance when not in use, as this will force you to reset the clock every time you want to use the microwave. Keep the ventilation slats at the back of the unit clear of dust; overheating the control board can lead to erratic behavior in the digital display and clock timing. If the display shows "Err" alongside the 0:00 reset, this indicates a deeper sensor failure and the unit should be serviced immediately.

Question 4

how do i clean the inside roof of this microwave? it has that brown splatter and won't come off.

Accepted Answer

DIAGNOSIS The splatter is baked-on grease and food. The stainless steel interior can be cleaned, but the textured 'roof' around the light and vents is tricky. FIX Heat a bowl of water with a few tablespoons of white vinegar for 3-5 minutes until the cavity is steamy. Let it sit 5 minutes. Use a soft cloth or non-abrasive sponge with the warm vinegar water and a drop of dish soap to wipe. Avoid the metal grill of the vent. IF THAT DIDN'T WORK For stubborn spots, make a paste of baking soda and water. Apply it directly to the stain, let it sit for 15 minutes, then gently scrub with the soft sponge. HEADS UP Never use abrasive pads, steel wool, or harsh chemicals like oven cleaner. They will damage the stainless finish and can create fumes next time you cook.

Question 5

my smooth wave makes a loud humming or grinding noise when it runs, not the normal fan sound.

Accepted Answer

DIAGNOSIS The loud humming or grinding noise in the Breville Smooth Wave BMO850BSS is typically caused by a failure in the cooling fan assembly or an obstruction in the magnetron's ventilation path. Unlike the standard operational hum of the transformer, a grinding sound indicates a mechanical struggle. This usually happens when the fan motor bearings wear down, causing the blade to wobble and strike the interior plastic housing, or when a foreign object—such as a piece of plastic wrap or a stray food crumb—has bypassed the filters and lodged itself in the fan blades. To confirm the source, listen closely to the rear and side vents while the unit is running. If the noise fluctuates in pitch as the microwave heats up, it is likely a thermal expansion issue where the fan blade is rubbing against its mount. If the noise is a constant, rhythmic "clacking," it is almost certainly a physical obstruction. If the sound is a deep, vibrating drone that shakes the chassis, the fan motor mounts have likely perished, allowing the motor to vibrate against the metal frame. FIX To resolve this, you must clear the ventilation system and check for mechanical interference. Follow these steps precisely: Complete Power Down: Unplug the BMO850BSS from the wall outlet. Do not simply turn it off at the display; the high-voltage capacitor inside can hold a charge, so ensure the unit has been unplugged for at least 10 minutes before proceeding. Exterior Vent Clearing: Use a high-powered vacuum with a narrow crevice tool. Run the nozzle along the rear ventilation grille and the side slats. Focus specifically on the lower rear corner where dust tends to accumulate and clog the intake. Compressed Air Purge: Use a can of compressed air (duster) to blow short, sharp bursts into the vents. Aim for the fan housing to dislodge any debris that the vacuum couldn't reach. Fan Blade Inspection: Using a flashlight, peer through the rear vents. If you see a visible obstruction (like a piece of packaging), use a pair of long-reach needle-nose pliers to carefully extract it. Do not push the object further into the unit. Leveling Check: Ensure the microwave is on a perfectly flat, hard surface. If the unit is tilted, the fan motor shaft can sit off-center, causing a grinding noise. Use a spirit level and adjust the feet if necessary. IF THAT DIDN'T WORK If the cleaning process does not silence the unit, the issue is internal and requires more advanced intervention: Bearing Lubrication: If the grinding is caused by dry bearings, the fan motor needs a drop of high-temperature synthetic lubricant. This requires removing the outer chassis to access the fan motor shaft. Apply a single drop of silicone-based lubricant to the motor bearing; avoid using WD-40 as it can attract more dust and degrade over time. Fan Blade Replacement: If the plastic blades are warped or chipped, they will create an imbalance that sounds like a grinding noise. You will need to source a replacement fan blade assembly specifically for the BMO850 series and swap it out. Magnetron Fan Alignment: The magnetron has its own dedicated cooling fan. If the mounting screws have vibrated loose, the fan will rattle. Tighten the mounting brackets using a Phillips #2 screwdriver to ensure the motor is seated firmly against the chassis. Transformer Mount Inspection: If the sound is more of a "hum" than a "grind," check the high-voltage transformer mounts. If the rubber dampeners have hardened or cracked, the transformer's 60Hz vibration will transfer directly to the metal shell, amplifying the noise. Replacing these rubber grommets will restore quiet operation. HEADS UP Keep these maintenance tips in mind to prevent future noise issues: Clearance Requirements: Ensure there is at least 4 inches of open space behind the unit and 2 inches on the sides. Restricting airflow forces the fan to work harder, leading to premature bearing failure. Avoid Steam Build-up: When heating very moist foods, ensure the vent is not blocked by towels or other kitchen items, as excessive moisture can lead to corrosion on the fan motor shaft. Warning on Capacitors: Never open the main chassis unless you are trained in discharging high-voltage capacitors. The BMO850BSS contains components that can deliver a lethal shock even when unplugged. Regular Dusting: Vacuum the rear vents once every three months to prevent "dust bunnies" from migrating into the fan housing.

Question 6

the control panel on my breville microwave is completely unresponsive, no lights, nothing.

Accepted Answer

DIAGNOSIS Total power failure. The most common cause is a tripped thermal fuse inside the unit or a loose power cord connection at the wall. FIX Check your kitchen circuit breaker or GFCI outlet first. Unplug the microwave from the wall, wait 60 seconds, then plug it firmly into a different, known-working outlet. Listen for a faint hum or click when you plug it in. IF THAT DIDN'T WORK If other outlets work, the microwave's internal thermal fuse may have blown due to overheating. This requires disassembly to check and replace—not a user-serviceable part. HEADS UP Don't repeatedly plug and unplug it trying to get a response. If it's completely dead on a good outlet, it needs professional diagnosis; attempting to bypass fuses is a fire hazard.

Question 7

why does my breville smooth wave smell like burning plastic when i use it?

Accepted Answer

DIAGNOSIS You're likely smelling overheated plastic from a foreign object inside the cavity or a packaging tag left on the unit. It's not the microwave itself burning. FIX Immediately unplug it. Do a thorough visual inspection inside the cavity and on the waveguide cover (the mica plate on the right wall). Look for melted plastic wrap, a twist-tie, a sticker, or any small object. IF THAT DIDN'T WORK If the cavity is clear, the smell could be coming from the vent system if it's new. Run it on high for 2 minutes with a bowl of water and lemon slices to clear manufacturing residues. Ensure nothing plastic is on the exterior vent slots. HEADS UP Never run it empty. If the burning smell persists after cleaning, stop using it—it could indicate a serious electrical fault requiring service.

Question 8

my breville smooth wave microwave just beeps three times and won't start cooking, what's the deal?

Accepted Answer

DIAGNOSIS The microwave is detecting the door isn't fully closed or the latch switch is failing. Three beeps is its standard 'door open' alert. FIX First, check the door is firmly shut—listen for a solid click. If it seems fine, inspect the door seal and latch area for any food debris blocking it. Wipe the inner door frame and latch clean with a damp cloth. IF THAT DIDN'T WORK The door latch microswitch might be faulty. Gently press the door latch mechanism with your finger while trying to start it. If it works with pressure, the switch is worn and needs professional replacement. HEADS UP Don't try to operate it if you suspect a faulty switch—the microwave won't run with the door 'ajar' for safety, but a failing switch can be intermittent and frustrating.

Breville Smooth Wave BMO850BSS Microwave

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