I have a Sta-Rite SR400NA 400K btu unit and I'm having a problem. The heater fires, runs for about a minute and stops heating. it restarts about a minute later and continues this cycle. The HLS LED was lit so I replaced the High Limit Switch and it worked for a few days and now the problem has returned. Any suggestions are appreciated. I hate to buy a new control board unless I can be sure that's the problem.
[Edited to add model number]