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Thread: Jandy (Laars) LT 400N-L Problem

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    Jandy (Laars) LT 400N-L Problem

    I have a Jandy LT 400N-L heater that was installed with the pool was rebuilt in 2005. It has never worked right. It would run fine for a few months then begin to shut off within a few minutes after igniting. I had some "Authorized" service people out who first said it was a pressure switch problem, charged me for a new switch after which the problem would come back a month or so later. Another service man put in a new flame sensor, but that didn't help. I am getting a flashing light next to the "pressure switch" indicator. I'm pretty handy with most things but I'm not sure where to start looking for the problem. Anyone out there familiar with this model and this problem?

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    Re: Jandy (Laars) LT 400N-L Problem

    I found a post from jkalan with what was supposed to be a link to the Jandy LT troubleshooting guide, "PoolCenter at Ideal BB" with a url of "", however, when I attempt to go there I get a 404 Error message, page not found. If anyone has an update to this troubleshooting guide I'd appreciate it.

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    Re: Jandy (Laars) LT 400N-L Problem

    After shutting down the whole system (I have a Jandy AquaLink RS with a PDA) I restarted it and the blinking red light next to the "pressure switch" went out when I turned the heater on. The blower kicked on high and after a few seconds the burners ignited. After about 30 seconds the burner shut off and the fan dropped down to low speed. A few minutes later the fan went back to high speed and the burners ignited again. Several seconds later the same shut down occurred. It did this once more and then the "AGS" light and the "Service" lights came on.

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    Re: Jandy (Laars) LT 400N-L Problem

    I've read several posts about cleaning the valves of any debris or spider webs so I took all of them off and found a few with blockage. After cleaning all the valves I restarted everything and now I'm getting the "Pressure Sensor" red light again. I suppose I'll go buy a new one on Monday and install it and see what happens.

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    In the Industry

    Join Date
    Jul 2011

    Re: Jandy (Laars) LT 400N-L Problem

    If your heater is located below water level the pressure caused by the water above the unit can trip the pressure switch and cause it to register water flow when in fact there is only water pressure.

    In the case where the heater is situated on an equipment pad that is below water level the installer should plumb an actual flow switch in line and wire the pressure switch wires to it. Flow switches have a swinging flap that registers when water is actually flowing through the plumbing. Pressure switches register when water pressure increases to a preset pressure. That pressure can also be created by the weight of water above the unit in the case of below water level installation.

    C-53 Pool Contractor.

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