The microwave does not heat, what to do: causes and solutions

Household appliances are not only comfort and convenience, but also a headache if something does not function.For example, you urgently need to heat up frozen food, and suddenly the microwave heating does not work.

Any modern electronic equipment is complex in design and operating principle; you have to carefully understand the reasons for failure step by step.

Why doesn't the microwave heat up?

It is possible to reliably determine the reasons for the lack of heating only by sequentially checking all the most important elements of the microwave. Therefore, the process of diagnosing the reasons why it does not heat microwave, must be divided into 3 stages:

1. We check the list of the most common reasons why a microwave may not work (this is approximately 80% of all cases of failure).
2. We consider external factors that do not depend on the condition of the microwave.
3. If you have not found the reason why the device does not work, you will have to check the most vulnerable components of the microwave.

In about half of the cases, the microwave stopped heating due to external reasons. For example, a lock is triggered, the power cord is broken, dirt and grease get inside the microwave unit. If the stove has a grill, then the problem may be related to the destruction of an overheated part or melting of the contacts or shorting of the insulation.

Common Simple Problems

The search for a breakdown should begin with the simplest cause. For example, a break in the power cord, a wire inside the cable, or at the power distribution point with a fuse. You can use a multimeter to check, but first you just need to move the cord. If the light appears inside, the fan and heating work, it means they change the cord, and at the same time check how the outlet itself works.

Insufficient voltage

If heating does not appear, then it is necessary to determine whether electricity is flowing into the microwave and measure the supply voltage at the input terminals of the power supply.

To do this, you need to unplug the microwave, place it in the idle position, unplug the cord from the outlet, and open the door to ensure that the heating is blocked if the device accidentally starts working while removing the lid.

Next, find the sealing point of the power cord and check the voltage. If there is no network, plug the plug into another socket and check again whether the heating works. If not, replace the cord.

The microwave may not be working due to low voltage. This happens if the house is located in the suburbs or in a rural area. It’s even worse if the voltage in the network “jumps” due to the fact that neighbors regularly turn on a powerful circular saw, electric boiler or heater in the bathhouse. In this case, a zener diode or a system of several relays on the input circuit of the power supply may fail.

The stabilized power supply is designed for a lower voltage threshold of 180 V, so for stable heating you will need to connect the microwave through a relay or slide voltage stabilizer with a power of at least 3 kW.

Technical difficulites

In addition to easily eliminated and obvious reasons why a microwave oven has stopped heating, there are hidden damages (mechanical and electrical). For example, the fan, cooling magnetron and radiator burned out.

Without blowing off the power unit (magnetron and transformer), the microwave does not work, and even if the “cold” device starts, the heating will work for a few seconds, after which the thermal relay will operate.

Door

Often the reason for the lack of heating is a sensor or contact that unblocks the power when the door is closed. After all, heating in a working microwave only works when the chamber door is closed.

There are 2 possible situations:

1. The latch with the contact is stuck in the “open” position due to accumulated grease. This means that the supply circuit is broken. The heating will not work in any door position.
2. The latch is stuck in the “closed” position. The most dangerous situation. The electrical circuit of the sensor that controls the heating operation becomes closed.

In this case, if you accidentally or carelessly open the door, you can get severe burns from the microwave magnetic field while the microwave is operating. Therefore, during any checks of the heating operation or simply the power cord, the voltage at the contacts, the door must be closed before starting.

Wrong mode

Heating may stop even while a seemingly working microwave oven is operating. For example, they put cold food in the chamber and turned on the heat. But in the end it turns out that the microwave oven does not heat the food. Ice crust does not conduct electricity.

The problem lies in the microwave device itself.For heating to work, it is necessary that the emitted microwave waves are absorbed by products, converting electromagnetic energy into heat.

If you select the wrong mode, a situation will arise in the chamber where the microwave operates but does not heat. The emitted microwave energy is not absorbed (very dry, heavily frozen or dehydrated foods). This situation is also called a reflected wave or lack of magnetic flux cohesion.

As a result of the microwave operation, heating does not occur, and all energy is discharged to the magnetron and high-voltage transformer. A few seconds of operating a Samsung or LG microwave in this mode is guaranteed to damage the magnetron. Some models, for example, Orion, will simply stop heating food to the desired temperature.

Complex problems

In order to restore heating, you will need at least:

1. An electrical diagram detailing the components used, electronic components, indicating the brand and denomination.
2. Multimeter for checking parts and measuring voltages (current).
3. Screwdriver with interchangeable slotted and cross-head bits.

You can work with a microwave oven only if the warranty from the service workshop has expired (or is absent). Household appliances, like a microwave oven, are repaired by replacing entire components, and their cost is quite high.

In some cases, for example, for Samsung microwaves, delivery of parts must be ordered and waited for weeks. Therefore, experiments with repair and restoration of heating are allowed only on old microwave ovens.

Fuse

Any microwave has at least 2 of them, but there can be 3 if the design has a grill.But only the fuse at the power supply input and another one, a high-voltage device that protects the HV transformer, are responsible for microwave heating. To check whether the fuse is the cause of the breakdown, it must be removed.

To get to the fuse, you need to remove the back or top cover of the case (different models of microwave ovens have different access to the components). The mains fuse is installed on the terminals next to the power cord contacts. You need to remove it and check with a multimeter for a break.

If you don’t have a device, you can check the heating by temporarily shorting the contacts. If the heating of the microwave works, then replace the blown fuse with a new one.

The second fuse is installed in the circuit between the magnetron and the high-voltage transformer. As a rule, this is a plastic tube body. Inside there is a glass fuse with a fuse link.

If destruction occurs, then on the surface of the glass you will see dark points where the insert burns out and a spring that has moved to one side.

The high-voltage fuse is calibrated by resistance at the factory during the manufacturing process. Therefore, it is purchased for a specific microwave model. Any attempt to short-circuit the contacts of the HV fuse to check whether the heating will work will lead to damage to the transformer or magnetron.

Magnetron

The most difficult to diagnose. The magnetron is designed to generate electromagnetic waves in the microwave range, providing heating of products in the chamber. If the power supply to the high-voltage transformer is unstable, the magnetron will overheat.

In order for the device to operate at the same temperature, it is installed on an aluminum radiator, plus the blower fan works.Therefore, if there is no heating and the fan does not work, then most likely the problem is in the magnetron, and specifically in the capacitor inside it.

Magnetrons can only be repaired in a specialized workshop. You can try to fix the breakdown yourself, but the device will still not work like new, and if the repair is poor, the microwave may catch fire.

Mica plate

The size of the part may vary, thickness 0.6-1.1 mm. The mica plate covers the window of the waveguide, through which microwave radiation passes from the magnetron into the chamber with the products.

If necessary, the mica can be temporarily removed. Any new microwave oven can operate without a mica screen. But the heating will be uneven and it will not heat well. Over time, the mica burns out (due to the heating of fatty deposits on it), accordingly, all water-fat evaporation gets inside the waveguide and magnetron. The stove begins to work with sparks and noise. As a result, everything ends in damage to high-voltage parts.

The plate can be bought at any workshop, you just need to know the dimensions.

Capacitor

There are 2 of them in the microwave. One is installed on the input block after the fuse and serves as a surge protector. The dimensions of the capacitor are large, the capacitance is usually measured in tens of microfarads.

The accumulated charge is enough to cause a strong electric shock if you touch it with your hand. Therefore, before disassembling and checking the parts, be sure to remove the cord from the network and close the contacts on the capacitor (discharge).

If a spark “clicks” when you touch it with a screwdriver with an insulated handle, then the device is working properly. The part can be checked using a multimeter.

The second high-voltage capacitor is located in the circuit next to the transformer.Most often, this is why the heating in the microwave does not work. It is necessary to dismantle and measure the resistance.

Diode

A high-voltage diode is installed next to the capacitor. It is difficult to determine whether a part works or not in everyday conditions. The only sign indicating a malfunction is burning or high resistance, both in direct and reverse polarity.

Timer

Heating often disappears in microwaves with a mechanical or electromechanical timer. If the model is old, then a huge amount of dirt has accumulated inside the device. The timer simply may not work due to blocking of the electromechanical drive by fatty deposits.

In electronic models, the timer is connected to the control unit, so heating problems are associated with a malfunction of the controller or memory chip in which the mode and operating time of the magnetron are recorded.

Transformer

The most vulnerable part of any microwave oven. The voltage at the output contacts of the transformer reaches 4000 V, so overheating can cause partial or complete breakdown of the insulation.

In the first case, the heating of the microwave may work, but with a strong smell of burnt insulation and a hum. This means that you need to block the operation and turn off the oven until other parts along the chain burn out.

If the resistance of the high-voltage winding is less than 150 Ohms, then the part must be replaced. On the “primary” of the transformer, the winding resistance should be 2.3-3 Ohms.

Inverter

To stabilize and equalize the voltage in front of the multiplier and high-voltage transformer. If there are signs of burnout, it must be replaced without repair.

Control block

In modern microwave ovens, time and heating power are controlled using several sensors and controlled relays (thyristor switches) connected to the control board.

There are 2 possible situations:

1. One of the sensors or thermostats is not working. In this case, heating of the products may be short-term, since the sensor sends an erroneous signal to the control unit that the limit temperature has been reached.
2. The control unit itself does not work.

The front part may be equipped with touch panel or regular buttons. If you cannot switch the heating mode by pressing the sensor or the digital display shows an incorrect value, then the problem is clearly in the unit.

The control board with buttons breaks less often. Push-button control may not work only if the wire is broken or the silicone cuff that protects the contact point from contamination is damaged.

You should not try to start heating without a unit; there is a risk of overheating and damage to the working components of the microwave. Electronic components of microwave ovens cannot be repaired.

DIY repair

The microwave is designed and manufactured in such a way that if it is used incorrectly or the heating power is exceeded, the least valuable parts will break. First of all, fuses. But sometimes there may be more reasons why a device does not work.

First, we remove the casing lining, leaving only the front panel with the door.

You can see parts behind the high-voltage transformer; damage to any of them leads to a situation where the microwave seems to be working, the panel lights up, but there is no heating. This is a high-voltage fuse (in a red housing), a capacitor and a diode.

Checking the high voltage fuse

Always checked first.First you need to discharge the capacitor. We attach the crocodile to the case, and with the other end (a probe with a resistance of 10 megohms) we touch the contacts on the capacitor.

Next, disconnect (remove the terminals) the housing with the fuse and divide it into 2 halves. Call immediately. If the device shows a break, it means that the magnetron is left without power, and there can be no heating in principle.

This is what a whole fuse looks like, the spring is stretched to its full length.

And so - burnt, the spring is not visible, there are traces on the glass from the evaporated metal of the fusible insert.

The design of the fuse is such that at the moment of burnout, the spring stretches the contacts, preventing an arc from forming. Otherwise, when the food was heated, the transformer and magnetron would burn out.

Capacitor check

The next step is checking the capacitor. If, when touching the probes to the terminals, the multimeter shows a breakdown, then the capacitor is definitely damaged.

There is a ballast resistance inside the capacitor, which discharges the remaining charge after heating stops. Therefore, the device shows not “0”, but 2 MOhm. The capacitor needs to be replaced, it can be a new one, but it’s better to use a used one. They are removed from microwaves that will no longer work and sent for disassembly. Their quality is no worse than new ones.

To check the capacitance, set the multimeter to the measurement limit of 20 MOhm, after which you need to touch the contacts with the probes. The readings on the device should increase, indicating charge accumulation.

You can put the part in the microwave and check the heating. But when choosing a capacitor you need to be careful; all those that pass the test will work, but not everyone fits inside the microwave body.

Checking the high voltage diode

It sits directly on the capacitor.You can remove the terminal and send it for testing. The high-voltage diode is designed for an operating voltage of 4000 V, so you can check how the device works against internal leakage.

You need to put a multimeter on the continuity test and check the diode in the forward and reverse directions. If the diode is working normally, the device will show a break.

The diode can be checked by connecting it to the network through an incandescent lamp. The light should flicker dimly. This means the diode is working.

Checking magnetron protection

Another reason why heating may not work is a blockage of the device generating the microwave field. The magnetron gets very hot during operation, so a thermostat is installed on it (usually on top). In the normal position the device is closed. If the magnetron overheats due to prolonged operation at maximum mode, the thermostat opens the contacts.

You need to remove the protective covers and ring the device. If the multimeter shows a short, then the thermostat and, most likely, the magnetron are in working order.

Checking the door sensor

The reason why the microwave heating does not work may not be hidden in electronic parts. Therefore, it is imperative to check the door closing sensor. In addition to the latch that secures the door, the lock is equipped with a microtoggle switch or “micrik”. The device contacts are laid out so that you can check how the blocking works.

The microtoggle switch can become sour from dirt, but more often the terminal on the contact simply falls off. If the chip is loose, then you need to lightly compress the terminal. Next, we connect the device for dialing and open and close the door several times; if the microtoggle switch works (closes and opens the circuit), then the problem of lack of heating lies elsewhere.

At the same time, you can check the status of the mains fuse. But this is more of a reinsurance. If everything in the microwave works except heating, then the mains fuse is also in working order.

Having completed all repair operations, you need to assemble the microwave and check how the heating works. To do this, pour water into a cup, place it in the chamber and start heating at medium power for 40 seconds. If the water has heated up, it means that all components of the microwave are working.

Fault prevention

A microwave oven is a rather complex device. Many components and mechanisms require regular maintenance. Moreover, many parts are made of inexpensive plastic and have a thin protective coating.

A microwave can operate for up to 10 years without major breakdowns, providing stable heating of food without major repairs. But only if during operation the stove owners adhere to the following rules:

1. If the network voltage is unstable, then the microwave must be connected through a voltage stabilizer.
2. Do not connect in the same line with boilers or washing machines, especially when heating products for a long time at maximum power.
3. When heating any food, especially frozen food without packaging, you need to use a special container with a lid or a plastic cap. Wash the walls of the chamber regularly to remove plaque.
4. Do not operate without a mica plate.

If you need to check how the heating works, be sure to place a glass glass or ceramic cup with water inside the chamber.

It is strictly forbidden to turn on the stove with metal objects inside. Even foil or a regular spoon can cause damage to the transformer.If you're lucky, experiments with heating will end with a blown fuse.

You need to wash and clean the microwave sparingly, preferably without a large amount of detergents. The enamel inside will not be damaged, and the microwave will not stop working, but it is still better to protect the electronics from contact with soapy water.

To ensure that your microwave can operate for many years, try not to cook in a microwave oven those foods and dishes that can be cooked on a regular gas or electric stove. Even if the recipe recommends microwave.

If you regularly run the stove for 30-40 minutes at medium and high power, then within a year the heating efficiency will decrease, the insulation will crack and smell, and after another couple of years the device will stop working.

And what you definitely shouldn’t do is dry things, shoes, or check how the heating of various objects works. The microwave is designed for food only. Any experiments force it to work in an off-design mode, which always leads to breakdown.

There are as many reasons why the heating of a microwave oven does not work as there are parts inside it. Each node can cause a malfunction, so the system must be repaired by sequentially searching through all possible causes.

Tell us about your experience in repairing a microwave oven, how you managed to restore the heating, what problems you encountered while working with the microwave oven. Save the article in your bookmarks, perhaps it will be useful to you in the future.