Rules to play Hot Air Ballooning
The burner is designed to create enough heat to warm up the balloon quickly. It is most efficient only when wide open. There is no good way to maintain the exact temperature required to maintain equilibrium.
Add to that the fact that when a hot air balloon is not actively being heated, it is cooling off. This means that it is in perfect equilibrium only momentarily. The rest of the time it is either too warm or too cool and so either climbing or descending.
These two facts together mean that under most conditions level flight is anything but. The goal of the pilot is to light the burner at the right interval and for the right duration (a few seconds) to keep the balloon slowly drifting up and down about the desired altitude.
An exception is made when flying close to the ground, as in an approach to a landing. Then the burner may be lit for very short bursts at a much higher frequency, thus sacrificing efficiency for accuracy.