If the dishwasher does not heat the water, the wash cycle is interrupted or runs in cold mode, which leads to poor removal of grease and food residues. The main culprit for such a malfunction is most often a burnt out heating element, but the problem may also be hidden in the failure of the thermostat, flow sensor or control module. The lack of heating of water directly affects the effectiveness of detergents, which are activated only at a certain temperature, so ignoring the symptom quickly turns dishes into a breeding ground for bacteria.
Primary diagnostics begins with checking the presence of electricity on the heating element and visually inspecting the contacts. In some cases, the machine may simulate operation by starting the pumps, but not issue a command to turn on the heater due to an error in the self-diagnosis system. It is important to understand that modern models Bosch, Electrolux or LG can block the program from starting if sensors detect anomalies in the water supply system.
The main reasons for the lack of water heating
The lack of heating of water in a dishwasher is often due to physical wear and tear of the heating element. Scale formed from hard water creates a heat-insulating layer, causing heating element overheats inside and burns out, ceasing to pass electric current. Visually, swelling, cracks, or characteristic black spots may be visible on the element, but the integrity of the spiral does not always guarantee serviceability.
The second common cause is a faulty thermostat or temperature sensor. If the temperature control device is “stuck” in the “heating on” position, it does not send a signal to turn on the heating element, even if the water is cold. Conversely, if the sensor shows a false temperature rise, the control module forcibly turns off the heating to avoid an emergency.
⚠️ Attention: Before any diagnostics, be sure to disconnect the dishwasher from the electrical outlet. Working with live electrical components is fatal.
It is also worth considering the operation of the pressure switch or water level sensor. If the machine does not “see” enough water in the pan, it will not turn on the heater to avoid a dry start. A clogged filter or water intake hoses can result in the required pressure not being created and the heating cycle simply does not start.
- 🔥 Burnout of the nichrome spiral inside the heating element due to power surges.
- 🌡️ Failure of the thermostat or oxidation of the temperature sensor contacts.
- 💧 Insufficient water pressure in the water supply system to activate the flow sensor.
- 🔌 Broken wiring or poor contact in the heater terminal block.
Diagnostics of the heating element (heater)
Check heating element is the first step in identifying the reason why the dishwasher stopped heating the water. To carry out accurate diagnostics, you need a multimeter switched to resistance measurement mode (Ohms). After removing the bottom panel of the machine and gaining access to the heater, you need to disconnect the terminals and measure the resistance between the contacts of the element.
The normal resistance of a working heating element for dishwashers is usually from 20 to 40 Ohms, depending on the power of the specific model. If the multimeter shows one (infinity), it means that the spiral inside is broken, and the element must be replaced. Zero resistance indicates a short circuit in the turns, which also makes the part inoperable.
☑️ Checklist for checking the heating element
It is also important to check that there is no breakdown in the housing. To do this, one multimeter probe is applied to the contact of the heating element, and the other to a metal tube or machine body. With proper insulation, the device should show infinity. Any resistance reading indicates an insulation failure, which can lead to knockout RCD or electric shocks.
Sometimes a heating element may be electrically functional, but not heat due to mechanical damage or severe contamination. A thick layer of scale prevents heat transfer, and the water inside the machine remains cold, although the indicators may show the heating process. In such cases, it is recommended to either perform an acid wash or replace the element with a new one.
Checking the thermostat and temperature sensors
The thermostat in the dishwasher acts as a regulator, opening the circuit when the set temperature is reached. If this component is faulty, the circuit may remain open continuously and the water will not heat. In modern models, instead of a mechanical bimetallic thermostat, electronic ones are used NTC sensors, the resistance of which varies depending on the temperature of the medium.
Diagnosis of the thermostat is also carried out using a multimeter. When cold, most thermostat contacts should be closed, indicating zero resistance. When heated (for example, with a hairdryer), the contacts should open and the resistance becomes infinite. If there is no response to heating, the component is considered defective.
Electronic temperature sensors are often integrated into the flow heater or installed separately at the bottom of the chamber. Their verification consists of measuring the resistance at a known temperature and comparing the readings with tabular data for a specific model Siemens, Candy or Indesit. A deviation of values by more than 10-15% indicates the need for replacement.
NTC sensor resistance table
At 20°C the resistance should be about 20 kOhm, at 50°C it should drop to 5-6 kOhm. The exact values depend on the sensor manufacturer.
Incorrect operation of the temperature sensor can lead not only to a lack of heating, but also to boiling water or damage to the plastic parts of the machine. The electronic control module relies on sensor readings, and if they are false, the operating algorithm goes astray. Replacing the sensor often requires complete disassembly of the lower part of the unit.
Control module and wiring faults
If the heating element and thermostat are working properly, the problem may lie in the control module or power circuit. The control board contains relays that switch voltage to the heater. Over time, the relay contacts can burn or stick, which is why the heating command is not physically executed, although the program is logically executed.
A visual inspection of the board allows you to identify blackening, swollen capacitors or traces of burning in the area of the heating element relay contacts. Often the fault lies not in the processor itself, but in the power elements. Repairing a module requires soldering skills and knowledge of electronics, so at home they often resort to replacing the entire board or contacting service.
The wiring connecting the module to the heating element is also subject to wear. High temperatures and vibration during spinning can lead to burnout of contacts or fracture of wires at the bend. It is necessary to “ring” the entire circuit from the output from the board to the heater terminals to ensure the integrity of the lines.
| Component | Problem Symptom | Test method | Solution |
|---|---|---|---|
| heating element | Resistance infinity | Measurement with a multimeter | Replacement |
| Thermostat | No short circuit to cold | Calling contacts | Replacement |
| Relay on board | No voltage on heating element | Voltage measurement | Board repair |
| Wiring | Open circuit | Visual inspection and dialing | Recovery |
It is worth noting that power surges in the network often damage the electronic components of the module. To protect expensive equipment, it is recommended to use stabilizers or surge protectors with adequate power. Ignoring this rule may lead to repeated breakdowns after repair.
The effect of hard water and scale
Hard water is the main enemy of dishwasher heating elements. Calcium and magnesium salts settle on the surface of the heating element, forming a hard layer of scale. This layer has low thermal conductivity, which is why the heat from the coil is less easily transferred to the water, and the element itself overheats.
Regular use of dishwasher salt and special rinse aids helps soften the water and prevent the formation of deposits. If the machine has been running for a long time without salt, the scale layer can become critical, leading to local overheating and eventual burnout of the nichrome thread inside the tube.
⚠️ Attention: Using regular table salt instead of specialized salt can lead to rapid corrosion of the ion exchanger and failure of the water softening system.
To remove existing scale, you can use citric acid or special dishwasher cleaning products. However, if the layer is too thick, dry cleaning may not help, but will only peel off pieces of scale that will clog the pump filters. In advanced cases, it is more effective to replace the heating element.
Display errors and fault codes
Modern dishwashers are equipped with a self-diagnosis system that displays error codes on the display or signals them by flashing indicators. For example, cars Bosch may flash the “Finish” indicator or issue a code E09, which often indicates problems with the heating or temperature sensor. Models Electrolux can show code i30 or i40, associated with the Aquastop system and water intake, which indirectly affects heating.
Error codes allow you to narrow down the troubleshooting area. If the machine writes an error related to heating, but the heating element is intact, the problem is most likely in the control circuit or sensor. The decoding of the codes for each model is unique and is contained in the service manual.
Sometimes the error may be false, caused by a temporary network failure or power surge. In such cases, rebooting the machine helps: disconnecting from the network for 15-20 minutes. If, after switching on, the error recurs when starting the wash, hardware intervention is required.
Tip: Take a photo of the flashing lights or error code before resetting the power. This will help the technician or search engine accurately determine the problem.
Don't ignore car signals. Running a dishwasher without heating not only does not clean the dishes, but can also lead to the growth of bacteria in the filters and hoses, causing an unpleasant odor. Timely elimination of the cause extends the service life of the unit.
Self-repair or call a specialist
The decision to repair it yourself should be made based on the complexity of the breakdown and your skills. Replacing a heating element or filter are operations that are accessible to most users with a basic set of tools. However, repairing the control module or replacing complex sensors requires expertise.
If the dishwasher is under warranty, any DIY repairs will void the warranty. In this case, the only correct solution is to call an authorized specialist. Even a simple replacement of a part with your own hands can be regarded as a violation of operating conditions.
The cost of spare parts for dishwashers varies: a heating element is relatively inexpensive, while a control module or an original flow sensor can cost significantly more. Sometimes it is more economically feasible to replace a car if the cost of repairs exceeds 50-60% of the price of new equipment.
The main conclusion: 80% of heating problems are solved by replacing the heating element or thermostat, but only a multimeter can make an accurate diagnosis.
Why does the machine hum, but does not heat the water?
A humming sound indicates that the circulation pump is operating. If the water is cold, then the command to the heating element is not received. Check the thermostat and voltage at the heater terminals during the wash cycle.
Is it possible to wash dishes if the heating element is burnt out?
Technically the machine will work, but the quality of the wash will be poor. Fats will not dissolve and bacteria will not die. Additionally, the detergent may not rinse completely, leaving streaks.
How often should the heating element be changed?
The service life of the heating element depends on the hardness of the water. When using softeners, it lasts 5-7 years or more. Without water softening, the element may fail after 2-3 years of active use.
What should I do if after replacing the heating element the error does not disappear?
Perhaps the temperature sensor itself is faulty, there is a break in the wiring, or the problem lies in the control module. It is also worth checking whether the new heating element fits tightly to the body and whether air has entered the system.
Does the length of the hose affect the heating of the water?
A water supply hose that is too long can cause a drop in pressure, causing the flow sensor to not operate. However, the length of the drain hose does not affect the heating of already collected water if the pump is working properly.