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Deadband is also known as hysteresis and is the amount of a measured variable (pressure, temperature, etc.) between the point where a switch closes and then re-opens. It can be implemented is software if you have an analog input (i.e., open at 1.02 PSI, close at 0.98 PSI) or designed into a switching mechanism. Often the deadband of a switch is fixed and cannot be adjusted. A typical example is in a wall thermostat in your house.
If you have power to the unit, the standby light is on, and the red lights come on when calling for hot water, yet you have no hot water, then it sounds like you have a dead water heater. If you have red lights on when no water is called for, turn off the circuit breaker feeding the water heater. There is a problem. If the water is just not as hot as it was earlier, consider whether the groundwater temperature has dropped.