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Thread: Bad FNS Plus Filter Guage?

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    Bad FNS Plus Filter Guage?

    I have seen where gauges can go bad and only read ZERO. But is it possible for a pressure guage to go bad and never read correctly? My guage has seemed to be stuck on 16 lbs all summer long. My filter is a DE filter and I have only backwashed once which was back in June. Since early June the filter has continued to read 16 lbs which is one lb over the backwash reading.

    I can't believe that it has never raised since last year i had to backwash probably 3-4 times. The guage will drop back to zero and also drop to around 10 when the pool slide is on. I also think that there seems to be a little bit less pressure at the returns but maybe it is just my imagination?

    Can a pressure gauge be bad and give you a false reading?
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump

    NC KANSAS44

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    Mod Squad Bama Rambler's Avatar
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    Re: Bad FNS Plus Filter Guage?

    Yes a pressure gauge can move but give a false reading. Usually you can tell if there's something wrong because it won't go back to zero when the pump is off.

    It sounds like you're just not building pressure and the gauge is operating correctly. My gauge barely moves at all until right before it's time to backwash. If your pool is relatively clean then it could go several months before needing backwashing. Having said that it won't hurt anything to go ahead and backwash it.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Bad FNS Plus Filter Guage?

    I wonder if the lack of backwashing need this year is due to switching to a vacuum external of the filtration system? My pool is fairly small and normally i can vacuum everything with my pool blaster which has it's own bag. Regardless I think you are right because my guage does go to zero when off.
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump

    NC KANSAS44

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    Mod Squad Bama Rambler's Avatar
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    Re: Bad FNS Plus Filter Guage?

    That certainly has had some effect in the amount of backwash required.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Re: Bad FNS Plus Filter Guage?

    A separate issue but does anyone know how to replace this guage? Mine is so clouded it is impossible to read.
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump

    NC KANSAS44

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    Join Date
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    Re: Bad FNS Plus Filter Guage?

    Quote Originally Posted by Thinkly
    A separate issue but does anyone know how to replace this guage? Mine is so clouded it is impossible to read.
    Doesn't it just screw into the air relief valve?
    20K gal IG plaster pool, Manually chlorinated with 6% bleach, 1.5 HP Sta-Rite Dura-Glas II pump, Pentair FNS Plus 48 DE filter, Polaris 280

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