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Thread: Jandy 700 error 121 intermittent - no calcium

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    chezhed's Avatar
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    Jandy 700 error 121 intermittent - no calcium

    Did some searches but didn't quite find the answer....

    My 3-1/2 year old unit is giving me intermittent 121 error code which according to the manual is a low voltage issue in reversing cell. I just checked and washed the cell. It doesn't have any calcium buildup and was clear, though a bit brown that cleaned off pretty well.
    My question is since the error only occurs during reversing, which I believe is the "cleaning" cycle, is there really any great urgency in replacing this?
    I have been running this thing 50% 12 hours/day from early May into Oct and then 10% 6-8 hours/day Nov thru Mar and bumping up in April. Salt is kept in the 3000 range year round.
    My pool is the same age as the SWG and came with a 3 year Jandy ProEdge warranty....I'm gonna be a bit PO'd if this thing is out at 6 mos outside.....
    Oh, we just had 12 inches or rain in less than 12 hours last week and I had to shock my pool with 5 gal of bleach and add 80 lbs of salt to get back.
    11,000 gal + overflow spa, IG gunnite, Pentair 48FNS DE filter, Hayward SP3210X15 pump, CompuPool CPSC36 Chlorine generator, pool valet w/5 zones, Pentair LP heater

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    JasonLion's Avatar
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    Re: Jandy 700 error 121 intermittent - no calcium

    Error 121 is low cell current, typical of a cell that is wearing out. SWG cells can wear out in one direction before they wear out in the other direction. That sounds like what is happening to your unit. When that happens, they are usually very close to the end of their lifetime anyway. That isn't the only possibility, but it seems like the most likely. SWG cells have a lifetime of about 3 to 5 years, so yours is old enough that it could possibly be near the end of it's life.

    SWG produce chlorine in both "directions" (normal and reverse). The change in direction helps clean any calcium buildup off of the cell plates. Both directions are the same as far as the unit is concerned. With the cell only working in one direction, you will still produce chlorine, but only half as much as you would otherwise.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    chezhed's Avatar
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    Re: Jandy 700 error 121 intermittent - no calcium

    OK, makes good sense...so I can just crank it up for awhile until I get a replacement? Mine is the square version with the sensor plumbed separate. The replacements appear to have the sensor plumbed into them so I presume I would just plug the old sensor and put it in the new spot?

    And my filters are due for replacement as well it appears.....hate to see all this hit at once


    uggh...further research indicates the new 3 port version is not the same length and requires replumbing. Dang..my pvc plumbing skills stink....seems like I don't have much tolerance in fitting in these cells....I need slop
    11,000 gal + overflow spa, IG gunnite, Pentair 48FNS DE filter, Hayward SP3210X15 pump, CompuPool CPSC36 Chlorine generator, pool valet w/5 zones, Pentair LP heater

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    Re: Jandy 700 error 121 intermittent - no calcium

    You're right. The new cells require replumbing and you have to buy the kit with the cell and sensor included.. I would consider a new unit if it were me. You still have the front and back board that can go bad in the unit.
    25K aggregate IG, Intellipro, FNS48, Polaris 360, PG2000 fiber optic light source

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    chezhed's Avatar
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    Re: Jandy 700 error 121 intermittent - no calcium

    My error codes are coming and going....sometimes I get 121 in reversind and sometimes not....sometimes I get 120 in other. But if I unplug the DC power from the cell and replug it, I get an error and then it quits. I measured current at board....seemed awfully high at 33.6 volts....measured best I can on plug and it's at 17 volts.


    Got the new kit...length appears to be the same but the connecting ends are now a larger diameter. And my pool installer plumbed this really close....the outlet end connector is butted up to a three way valve! It now looks like I have to get a new valve as well and replumb the entire output from filter to return/water feature! And of course it's not all in the same plane.....I'm not real happy with my installer
    11,000 gal + overflow spa, IG gunnite, Pentair 48FNS DE filter, Hayward SP3210X15 pump, CompuPool CPSC36 Chlorine generator, pool valet w/5 zones, Pentair LP heater

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