Air-Fuel Ratio (AFR) Sensor
Tankless water heaters monitor and adjust their fan speeds to ensure that air and fuel remain mixed at the correct ratio. This is important to ensure proper combustion occurs at all times. This actively reduces emissions and increases efficiency.
Exhaust temperatures are monitored by your indoor condensing water heater to ensure that it operates at a safe level for PVC venting. If temperatures reach unsafe levels, combustion is regulated by the thermistor and hi-limit switch. These can even turn the water heater off to protect the venting material from damage. Learn more about vent configurations.
The hi-limit switch uses data from the inlet and outlet thermistors to make sure the water is at an appropriate temperature. If measurements exceed 185° F or 194° F, the hi-limit switch shuts down your tankless water heater by disengaging gas valves.
With an internal freeze protection system, tankless water heaters use electric heaters to prevent the heat exchanger's temperature from dropping too low. Some models boast additional protection that allows the burner to fire for a few seconds. These features reduce the chance of freeze damage. However, we recommend that a tankless water heater be installed indoors if you live in a cold climate so that it is not exposed directly to freezing temperatures.
Overheat Cutoff Fuse
Tankless water heaters are protected by a built-in overheat cut off fuse that disengages the gas valve if there is a breach in the heat exchanger wall or gaskets around the combustion box.