AGS Sensors.
The AGS sensor is just a switch that is either open or closed.
They are simple devices and rarely fail.
Unless your old one was corroded it is probably still good and was doing its job.
Confirm, using a multimeter, the AGS sensor is open when the heater is off before replacing.
The AGS trips (opens) when the internal water temperature exiting the heat exchanger is 140 or more.
It is a backup to the high-limit switch which is set to open at 135.
This is usually caused by too low a flow rate. Possibly a bad internal bypass or thermal regulator as discussed in the sections above.
If you do replace the AGS Sensor use a bit of Teflon tape to insure no leaks.
It doesn't matter which wire goes to which terminal on the sensor.
AGS Error.
AGS errors are usually caused by a bad internal bypass.
Too much water is bypassing the heat exchanger internally.
What water that is going through is coming out too hot and tripping the AGS switch in the manifold.
- Remove the leads from the AGS sensor and connect them together. Temp only for the test.
- Then, check the continuity of the sensor. It should be closed.
- Start the heater. If the sensor opens, immediately turn off the heater.
- If the sensor opens, it might be a bad sensor or the water is overheating.
- To test the sensor, put it in hot water to see where it actually opens.
- If the sensor does not open and the heater shuts off with an AGS light, the board is bad.
If the AGS LED comes on before the heater fires, then the AGS sensor is probably bad.
If it comes on only after the heater fires, then the thermal regulator might be bad or maybe a bad internal bypass.
Check the thermal regulator and look into the hole to check the internal bypass while you have the thermal regulator plug open.
