If it takes a long time to locate a signal or if the readings appear inconsistent:

1. Check that your belt is correctly positioned on your body. Also check that it's the right way round.
2. Check that you have dampened the sensors on your belt.
3. The HR signal can be affected by electromagnetic interference (power lines, railway, computers etc. When using your heart rate monitor, ensure you stay away from similar kinds of interference
4. Check that the battery is still charged.