I Have A Bosch Dishwasher That Is Not Heating The Water.

Regardless of whether it's plumbed into a hot or cold water supply, your dishwasher will have a heating element (visible in the tub) or a flow-through heater (which isn't exposed) that are used to control the water temperature and aid in the drying process.

Although the heating element is generally a very reliable component of a dishwasher, it can burn out or suffer from an electrical/wiring fault.

If you have a multimeter you can measure the resistance of your heating element which should read somewhere between 15 and 30 ohms. A reading above 30 means the element is faulty and will need to be replaced. If the resistance reading is OK then check the wiring and control board for damage.

A replacement heating element isn't massively expensive, and if you're comfortable getting your hands dirty then it's fairly simple to replace the part with a basic toolset.

The thermostat is the other component that can commonly cause your dishwasher to not heat the water. The job of the thermostat is to regulate the water temperature throughout a wash program. If it's faulty then the dishwasher won't "know" when to turn the heating element on and off to keep the water at the required temperature.

Just like the heating element, you can test the thermostat using a multimeter to determine whether or not it is the source of the fault. Luckily it's a very cheap part if you need to replace it, the only real difficulty is getting access to it as you'll find it underneath the dishwasher.

Whilst almost all dishwashers can operate using the cold water supply and heating water internally, many people connect their dishwasher to the hot water supply if their model allows it, as it can be more energy efficient and inexpensive (especially if you run a cold/no-drying program).

If you have your dishwasher connected to the cold water supply then it's highly likely that a faulty heating element or thermostat are the cause of the water not heating.

If you're connecting to hot then it's worth checking the water supply to check that there is actually an issue with the dishwasher and not elsewhere. Try running the hottest washing program to see if the dishwasher itself is able to heat the water to the required temperature.

As a side note it is worth paying close attention to the operating instructions if you connect your dishwasher to the hot water supply, making sure you don't exceed the maximum water temperature. Many modern models will also detect if the water entering the machine is already hot and shorten the duration of the wash cycle accordingly, which can result in sub-par cleaning.