Long time lurker, first time poster.
I have a Sta-Rite 400NA pool heater. For he the past month, the heater would work fine for an hour or two, and then flip to 'Service Heater'. I didn't bother taking it apart to check it (I know, dumb), and now it's to the point where I turn it on, it starts up, runs for about 10 seconds, then flips to service heater.
On the bottom of the board, the AGS light is lit red. In looking at the troubleshooting guide, it says to replace either the High Limit switch or the automatic Gas Shutoff switch. (no recent changes to any other pool equipment, so water flow should be fine). I've only owned the heater for a couple of months (moved in recently) so I don't know if either switch has been replaced - does anyone have any advice as to which one to try first (or if I'm totally approaching this wrong in the first place)? Each costs about $45 where I live so it isn't breaking the bank to replace both, but I'd really rather just do the one if I could.
Thanks a ton in advance!