Jandy Laars LX Pool Heater / 400,000 BTU / Natural Gas Logo
Brett Hoskins Posted on Mar 17, 2014
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Pressure switch light going off and heater won't start

I am having a pressure switch alarm on an lt400n-l heater

  • Gretchen Andrews
    Gretchen Andrews Mar 18, 2014

    I had this problem intermittently over a 3 year period and it was driving me crazy. I found I had two separate issues both having to do with wire connection that was preventing my flame to ignite. The first was actually in the Timer box. I found that I had corrosion build up on the ground connection that prevented the ignition. I fixed this by cleaning all connections in the timer box as well as taking the precaution that other connections could be building up the same corrosive issue, I cleaned all connections I could get at in the heater and attached securely. This seemed to have solved problem for several months but then again I had same pressure switch alarm return. This time I found that I had a break in the wire connected to the Flame Sense Rod. The wire was broke, but so little that it did not become completely separated. I was able to trouble shoot this by using a jump between the wire and the connector, this also served as temporary correction until I could order the replacement part. I recommend you take the rod completely out and clean it with an emery cloth to make sure it is also not corroded.

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Scott Corey-reid

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  • Posted on Mar 18, 2014
Scott Corey-reid
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Back wash filter. clean out pump basket, ensure you have proper water flow. Once you have ensure proper water flow and problem still exists, you will most likely have to replace the pressure switch

  • Steve Slater Apr 15, 2014

    You can put filter setting on "whirlpool", "bypass to pool", or "recirculate" (depending on filter brand). This will bypass water flow past the filter. If problem is resolved then the low flow issue is inside the filter.

  • Scott Corey-reid Apr 15, 2014

    if you put filter on recirc it bypasses the filter and wont clean the water wich is pointless. You have a faulty pressure switch, poor wiring, or you havntback washed filter in ages, or the sand in your filter needs to be changed, otur cartridge filter needsto be cleaned out

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I have a Big Maxx heater and it won't stop blowing and won't heat. The fan just keeps running! Anyone know what could be wrong?

Your pressure switch may not be activating (ie closing and making contacts) This means you could have a blocked flue, clogged pressure switch tube or a bad pressure switch. The pressure switch is a safety feature to ensure your exhaust is not blocked and operating correctly. Find owners manual. Look at trouble shooting section. Open cabinet and look for error code light. If blinking 3 times, try "jumping" the pressure switch. To jump pressure switch you need to clear code be turning off power. When the unit/thermostat calls for heat the power vent fan starts first, this is when you need to jump the pressure switch. You need to do this in sequence. That is the unit first starts the power vent exhaust thus activating the pressure switch allowing the ignition cycle to the burners and heat. So the power vent fan needs to start first BEFORE you put the jumper on to bypass the pressure switch. Once the jumper is on it will call for ignition after approx 30 seconds. If ignites your problem is one of the 3 stated at the opening of this paragraph
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"LO" is simply informing you that the Heater is not sensing proper water flow through it! A Flow Problem.
A special sensor, called a pressure switch is this source. But... That does not mean it is bad - No, it is in most cases just doing its job!
Most common reason - Dirty Filter.
A good cleaning of the cartridges, or maybe a breakdown and recharge of a DE Filter, or a good cleansing backwash of your sand filter, will remedy this situation.
Or... Check for any OTHER reason or situations water flow may be reduced through the heater:
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  • If you have a weir gate in skimmer, is it stuck in the UP position?
  • Are any valves closed?
  • Do you have a bypass valve at the heater?
    • If open, this will reduce the amount of water going thru heater, close it to the point, LO goes away.
  • Could be debris in front of Pressure Switch, in the copper tubing
    • Unscrew and remove pressure switch, turn pump on. But first, align end of tube so that when water squirts out it will shoot out from heater and not onto electronic heater components!
  • If all above is good, you may have failed pressure switch?
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Good Luck - hope this helped.
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The heater won't fire up if there is no or inadequate water flow. Ck water pump and filters.
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