Ags lite comes on

AGS = Auto Gas Shutoff...
What is happening is the heater is monitoring (or sorta, by reasons difficult to explain here) Water Flow and Water Temperature. In this case, the AGS is triggered by a low water flow, or high Incoming Water Temp.
High internal water temp = triggered AGS.
If you have and can confirm, PROPER water flow, water temp coming into heater is Lower than 104°, then it is possible you have a faulty AGS.
But in most cases, it's only doing its job. Locate the reason for the fault, or why the AGS Switch turned the heater off.

This issuesounds tricky. I recommend you call the Jandy technical support at 800-822-7933and they should be able to help determine what to do next. Ihope this helps.

you didn't indicate exact model but here is what the AGS is for.
Not sure if yours has a combustion blower or not, if so check that it's flow is not obstructed. If it doesn't make sure there are no debries in the flue area. Here is the troubleshooting from their manual. You can download a manual from www.jandy.com
AGS
(automatic gas shut-down)
1. Oscillating pump pressure. 1. Clean filter or identify and repair cause of pump
oscillation.
2. Low gas supply pressure. 2. Identify and repair incorrect supply pipe size or
pipe line blockage.
Refer to qualified service personnel.
3. No flame at burners. 3. Identify and correct loose wiring connections, or
problems with igniter, flame sensor , gas valve, or
ignition control.
Refer to qualified service personnel.

Sounds like the heater is dead, check to make sure your getting voltage to the inside of the unit, The power comes into the galvanized box, there is a fuse in there. Depending on how it was wired you should have 120 or 240vac

AGS MEANS TH EHEATER IS NOT FIRING CHECK YOUR GAS VALVE IF OPEN THAN CLEAN THE ORIFICES WHERE THE GAS COMES OUT AT THE GAS MANIFOLD

cycling usually begins as the result of poor water flow caised by debris in the pump, dirty filter or low water level. once you have had some cycling the heater burners and ignitor become sooted and this requires pulling the burner tray, de-sooting the burners and pilot and reassembly. unless you are very competent you may want to call a service tech. Pool heater repair is a high laibility endeavor if done improperly. During the certification class our instructor showed us several houses that were burned down from improper heater repair.