Question about Jandy Laars Lt 250,000 Btu Heater

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High Limit Swtiich message

I am getting a high limit switch message and the heater is not operating. Was working 2 days ago, nothing has happen to the system that should have changed anything. What does High limit switch mean

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  • 2 more comments 
  • pjdefelice Jan 03, 2009

    Our igniter fails to operate. Is there a way to clean or check it?.

  • Anonymous Jan 10, 2009

    What if you jump both High limits and are still getting this error. I'm also a technician but this one is driving me nuts. Pretty sure there is a clog in the exchange.

  • Miltonian May 16, 2009

    Had same problem with Service diagnostic message: Hi Limit Sw. When I pulled out both the 135 and 150 degree switches they appeared to have heavy white calcification after only 4 seasons. Tried cleaning then with isopropyl alcohol but did not work. Replaced with new ones one at a time at $37 cdn a pop each and after the new 150 was in the heater started working.

    Anyone know why I'm getting calcification and how to resolve it as don't want to fork out $80 every 4 years?


  • Anonymous Mar 31, 2014

    gas is on, control unit seems to work, when turned on to "spa" or "pool" nothing happens, ie no blower. after 2 or so minutes "high limit switch" error appears. I have checked and both switches are closed.



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The high limit switch is one part of a safety loop circuit that must work before a heater can fire. It's purpose is to ensure tha tthe heater will shut off in the event of a thermostat failure or if the internal core gets too hot due to a lack of water flow. If the switch is failing, it needs replaced. There are 2 so you can replace both or make an attempt to determine which one is bad. It is best to replace the pair.

Posted on Dec 21, 2008


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High limit switches are very cheap 1 time switches. They do not go out without a reason. When is the last time the heat exchanger was flushed? Has the burner tray been cleaned recently?
Is there enough water flowing through the heater? Is the heater and pump set on a timer?
If you have a sand or DE filter, do you backwash frequently enough?

All these things will affect the temperature of the outgoing water and the temperature of the high limit sensor(switch). I would say it is most likely flow related, but could be that the gas valve isnt tuned up too.
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Either heater is burned up, or high limit is bad. If you take dryer apart and get to heater you will be able to visibly see the broken heater wire. To check high limit switch disconnect the only two wires on the switch and using Ohm meter put one lead on each terminal. Should read closed if switch is good. High limit switch is located on panel covering heater coils If heater is not broken, and high limit switch is closed then you are losing power on your temperature control.

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To Test the limit switch put the wires together (if just 2 terminal) and see if it works. If so replace the switch assuming it is not a manual reset. REPLACE the switch, Don't just leave it by passed. If it has 3 or more terminals you will have to find the wire diagram and decide which terminals should be closed and if any should be open, or if the switch has some kind of built in heater on the part.

If the same thing happens you know its not this part but something else and you'll have to get a volt meter to start eliminating whats working from whats not and when its working to get to the bottom of the problem and finding what it is.

Please if this helps you rate me as high as you possibly can. Thank you for using fix ya.

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It may also be the high temp switches under the 2" inlet/outlet header. The 150 degree high-limit switch sits horizontal and corrosion happens often there. But be careful removing as if the header is corroded and the switch is also, water will flow out , so be ready to bypass the heater. You will have to replace the header. Try to jumpe that switch out and I'll bet the heater fires up.

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