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Jandy Lx400 Heats For 30 Seconds Then Stops - No Error Code


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My Jandy LX400 heats for about 30 seconds (blower starts) and then stops - no error is thrown in the console. It was working fine when I shut it down last year. After reading a number of posts I check connections, then checked the flame sensor connection and lightly sanded it to remove a bit of gunk, but that made no difference.

The LX400 manual mentions a throttle strip on the burner tray to allow more air into the combustion chamber - I can't tell where the strip is or whether it make sense that might be the cause.

I know I also saw mention of measuring the flow sensor current - is this possible without disassembly of some parts.

Many thanks,

Bruce.

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Those hi-limits attach to the outside of the header and aren't subject to the (corrosive effects of) water. That's not to say that they couldn't get corroded. The bypass assembly on the other hand is in the waterway, and would be my bet. Cost of By-pass is less than the hi limit kit (2). Note: Not to say i'm right Paul, but i don't see as many hi-limits fail as i do bypasses. One thing the OP can try is to bypass the hi-limits, run the heater, and if it begins to knock and/or bang, it is the by-pass or some kind of an obstruction, and not the hi-limit(s). Hi-limits usually react to another problem, not their own problem.

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Hi Guys - thanks for the suggestions.

When I bypass the hi limits the heater runs without issue. No knocking or banging. I had the high-limits replaced two years ago - when I open them up they are pristine - no corrosion, build-up or anything else untoward. And I measured resistance across the hi limits and it measured 0.

I repeated again just for good measure. Byoass hi limits and heater works (without any banging) - re-enable them and heater works for 30-45 seconds and then stops heating.

Is there anything I should/could try/test?

Many thanks,

Bruce.

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  • 4 weeks later...

It's taken some time to get back to this, but as it turns out the brass(?) posts that sit behind the hi-limit switch had corroded away, so I replaced them (created new ones from other on-hand spare parts, since last time I tried to order these they sent me the wrong thing). Replaced those posts and the high limit message went away. Of course I blew the inline fuse during testing and got a subsequent low pressure error - a few voltage tests and I knew to check the fuse. So, I replaced the fuse (about $0.60) and the heater starts up again! Thanks for everyone's help.

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  • 11 months later...
  • 2 weeks later...

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