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Thread: Heater w/ 2 speed pump question

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    mitch08's Avatar
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    Jun 2008
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    Heater w/ 2 speed pump question

    Hey guys,

    I just installed a 2 speed pump since I normally run my filter 24/7 for the summer and figure I can use the lower speed the majority of the time to save me money on electric.

    My heater is a mini-max 250. It is old but it still works like a champ. I just had my pool guy retrofit a digital thermostat to it, because I was having a tough time controlling the spa temperature. The digital therm works great.

    The only issue is that the heater will not stay on with the pump set to low speed. It does come on, but it cuts off after a few minutes. I assume it is because of the lower water pressure pushing through it.

    Now that I have a digital thermostat I can set, I want to just set the pool temp to a specific temp (85) and leave it. I feel like this will save me money in the long run since it will always be around that temp and I don't have to keep heating it from 75 (I live in NY and its usually around that temp in the morning) to 85 every morning when we are going to swim.

    Is there anything I can do to get the heater to stay on while the pump is set to the low setting? This way I can keep the pool set at a specific temperature and keep the pump running on low speed over-night?

    Thanks a million for any help!
    18x38 Inground Liner (25k gal) Paver surround, multi-speed pump, DE Filter, Raised spill over spa, TF-100

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    JasonLion's Avatar
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    May 2007
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    Re: Heater w/ 2 speed pump question

    The heater is turning off because there isn't enough water flow. Running the heater with insufficient water flow can damage the heater. It is remotely possible that the flow sensor in the heater is not calibrated correctly, but adjusting the flow sensor without a true flow meter is risky. If you set the flow sensor too low the heater can self destruct.

    It is possible that cleaning your filter or adjusting your valves might increase the water flow enough for the heater to work, but most likely there isn't anything you can do.
    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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    mitch08's Avatar
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    Re: Heater w/ 2 speed pump question

    Bummer that I can't do anything about it. I was hoping for a solution but I dont want to risk the heater so I will leave it alone.

    But thanks so much for answering so quickly... This website is incredible!!!
    18x38 Inground Liner (25k gal) Paver surround, multi-speed pump, DE Filter, Raised spill over spa, TF-100

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    frustratedpoolmom's Avatar
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    May 2007
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    Re: Heater w/ 2 speed pump question

    Mitch, I run my filter on low 24/7, and I have my heater set to 86 degrees. When my filter is dirty, the heater won't run, as it's pressure switch is very sensitive. My filter's pressure gauge won't change, but the heater's switch is apparently more sensitive. Sometimes when it wouldn't work on low speed, it would turn on at high speed. But after a short time, even then it wouldn't fire up. So I hose off the cart, and voila heater works again.

    So I would try cleaning your filter, see if that's an issue?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    budster's Avatar
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    Re: Heater w/ 2 speed pump question

    FYI, a dirty filter is the number one reason for heaters not running or not getting to set temperature.... 8)
    http://www.swimmingpool.com/

    "Leave the gun...take the cannolis"

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