hey_poolboy

Is this natural or propane?

High limits on that heater are located directly under where the plumbing goes in and out. There will be two silver cover plates over with philips screws that hold the hi-lims in place. Each will have two white wires. Remove them and do a visual inspection. With polymer headers there will be a brass bolt/nut that transfers the heat from the water to the face of the limit switch. If the limits are corroded at all check to make sure that those brass bolts aren't leaking into the limit area. IIRC the bolts are still available, and the limits are certainly available. Keep in mind, if the limits look fine, you can still check them for continuity with a meter. It is also possible that the wire has been broken. If the limits have actually had to perform their intended job they also have a life span. Jandy usually says about 10-12 cycles.

If you have an ozonator in it (especially a CD) try powering down, unplugging the ozonator then powering back up. sound weird, but I've had that happen before.