I have a Teledyne Laars Lite LLD325N heater. I am having issues keeping it burning. I did just replace the the bypass valve in the inlet/outlet header. The old one was stuck partially open and all corroded. I all replaced both high limit switches. Prior to doing this it would run for 12 mins and shut down and try retiring 2 more times. After the parts change now it will run for approx 24 mins and shut down. Doesn't matter if I have it turn to pool or spa. The HSI appears to be working ok cuz it lights fine. And from my research this is also the flame sensor. When it tries to re fire the burners kick on for a sec then go out. If I shut it down for a few mins and turn it back on it does the same thing. Before I get into buying more parts I was wondering if anyone has other ideas for me? I've done some testing of voltages and all seems good. The sensor in the header with the plastic tube around it, is this the temp sensor? Can I bypass for testing purposes? Also the thermostat, can I bypass that to test if it's good or not? Any help is appreciated. Thanks in advanced.