Balboa uses M7 technology in all control systems from the GS, GL and BP ranges: two identical sensors are mounted at the opposite ends of the heater and are used to determine the temperature, flow rate, and various error conditions. These two sensors replace failure-prone mechanical pressure/flow switches. They also act simultaneously as temperature and Hi-Limit sensors and compare the temperature of the incoming water with that of the outgoing water. This technology works regardless of the direction of water flow in the heater.
Older control systems with pressure switches use conventional temperature and Hi-Limit sensors.