Decreased supply temperature of district heating networks gives a number of system’s advantages, like increased overall efficiency, possibility to use renewable energy resources and decreased heat loss from the district heating network. To ensure the appropriate heat supply to the customers and avoid large pipeline diameters, it is important to keep the temperature difference as large as possible. Therefore the return temperature of the district heating network should also be decreased. When supply and return temperatures are lowered, the district heating network is more sensitive to the temperature difference faults, making fluctuations in the temperature graphs. Due to this fact it is important to predict behavior of district heating system’s temperature difference, depending on the outdoor temperature.