Buildings are responsible for 40% of our worldwide energy consumption and 50% of this energy is converted for HVAC systems in buildings, e.g. for hot water. In this paper, we will simulate the participation of a water heating system in the balancing of the electricity net. Here, the goal is to change the setpoint of the water heater and thus adapt the power consumption. The transmission system operator rewards active participation in delivering balanced energy. In our simulations, we replace a standard on/off controller with an economic model predictive control (MPC) controller that takes its optimisation, energy cost, and reward for delivering balanced power into account. The outcome will show that the economic benefits of participating in delivering balanced power is significant. We show that the choice of an MPC controller is valid as it allows the setpoint to change if certain conditions are met. Simulations show that the controller often decides not to participate in delivering balanced power because the conditions are not optimal. With a normal controller, this choice would not be possible to make, which would lead to a sub-optimal revenue stream from selling flexibility. Simulations show that the energy consumption goes up, which is permitted as the participation in net stabilisation allows the macro-system to integrate more renewable energy sources. Another conclusion is that the poorer the energy performance of the system, the more flexibility can be sold. From a policy point of view, a minimal energy performance should be determined before allowing participation in net stabilisation.