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Bosch Microwave not heating

When your Bosch microwave is not heating food, the most likely cause is a failed high-voltage diode. The diode supplies the magnetron with the voltage it needs to produce heat, and a burned diode may be visibly damaged or fail a continuity test. A defective door switch is the next likely cause because the microwave will not heat unless the primary, secondary, and monitor switches confirm that the door is closed. If those parts test good, the magnetron may be burned out and require replacement. A tripped or open thermostat can also stop voltage from reaching the heating circuit, followed by a failed high-voltage capacitor. Less commonly, the high-voltage transformer may fail, often causing arcing or a burning smell. A microwave that runs but doesn't heat requires caution. Any repair that involves the magnetron, high-voltage diode, high-voltage capacitor, high-voltage transformer, or opening the outer cabinet requires properly discharging the capacitor, which can store a lethal charge even after the microwave is unplugged. If you are not familiar with capacitor discharge procedures, use a qualified technician. Enter your Bosch microwave model number to find the exact replacement part for your appliance.

01 - Bosch Microwave Diode

The diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron to heat the food. If the diode burns out, the magnetron won’t receive enough voltage to operate, preventing the microwave from heating. When the diode fails, it is often visibly burned out. Inspect the diode and if the diode is burned out, replace it. If inspecting the diode proves inconclusive, test it with a multimeter that uses a 9-volt battery or put a 9-volt battery in series with the diode. When the leads are reversed, the diode should only have continuity in one direct...ion. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the diode.)
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02 - Bosch Microwave Door Switch

Most microwaves have three or four door switches. When the microwave door closes, the door switches actuate in sequence to ensure that the door is closed properly. If any of the door switches fails, the microwave will not start or heat. To determine if any of the door switches are defective, use a multimeter to test each of the switches for continuity. If any of the door switches does not have continuity, replace it. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremel...y dangerous to replace the electronic components in a microwave. Only a licensed technician should replace a door switch.)
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03 - Bosch Microwave Thermostat

If the microwave overheats, the thermostat trips to cut off voltage to the microwave. If the thermostat is shorted open, it may not allow voltage to reach the high voltage components. To determine if the thermostat is at fault, use a multimeter to test it for electrical continuity. If the thermostat does not have continuity, and it cannot be reset, replace it.
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Highly Likely

04 - Bosch Microwave Magnetron

The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the magnetron burns out, the microwave won’t heat. The magnetron is not repairable—if the magnetron is burned out, you must replace it. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the magnetron.)
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Highly Likely

05 - Bosch Microwave High Voltage Transformer

Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food. When a high voltage transformer fails, it will usually arc and have a burning smell. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the high voltage transformer.)
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Common

06 - Bosch Microwave High Voltage Capacitor

The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out, the entire high voltage circuit will stop working properly, and the microwave won’t heat. To determine if the high voltage capacitor is defective, use a VOM meter with a capacitance testing capability. (“Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerou...s to replace the electronic components in a microwave. Only a licensed technician should replace the high voltage capacitor.)
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Common

07 - Bosch Microwave Thermal Fuse

The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse doesn’t have continuity, replace it. The thermal fuse cannot be reset—if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse.)
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Less Common

Frequently Asked Questions

Why is my Bosch microwave not heating food even though it runs?
How do I test a Bosch microwave door switch when it is not heating?
Can a Bosch microwave thermostat cause the microwave to stop heating?
Is it safe to replace the Bosch microwave diode, magnetron, or capacitor myself?
How do I find the correct Bosch microwave replacement part?