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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  • 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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How to check high limit switch on theme Hester

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Limit switches keep going bad. Just replaced a week ago Got second time in about 3 month period of time. What could be making this happen?

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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Why does the display show "HI" all the time?

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There will be a pressure switch seated right on top of the header, then right below that, there are 2 high limit switches (1" round disks) Most typically, the pressure switch will start to leak and currode the contacts of the high limit switch, but some investigating will be necessary.

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(natural gas) the heater comes on for 3-5 minutes and then shuts off, and won't work again for hours. this is a shred heater between the pool and hot tub, but never used for the pool.

Check your high limit switch inside of the heater. Usually when the high limit switch pops it will take about 4 to 6 hours for it to reset itself without you resetting the system.

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