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Thread: Hawyard H400 Heater "LO" flashing

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    Hawyard H400 Heater "LO" flashing

    I recently bought a house with a in ground pool/hot tub combo that includes a Hayward H400 pool heater. It was a bank owned house where the pool had been sitting without filtering for probably 6 months. After getting everything cleaned up, having the system gone through, I fired it up and the heater cycled right on and i left it on for about 3 days heating the hot tub only. After leaving it off for about a week I came back and now it won't cycle on and gives me the "LO" diagnostic code on the LED read out. Pressure is good going into the unit so all I can figure is its 1 of a couple sensors that could either be bad or giving me a bad reading. I live in Arizona where the water is pretty dang hard. Where should I start in diagnosing this before calling the pool guy? Which if any of the sensors most commonly fail on these? Any help would be great!



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    spishex's Avatar
    Join Date
    Oct 2008
    Hillsborough, NC

    Re: Hawyard H400 Heater "LO" flashing

    LO is a low pressure/flow error. Be sure your filter is clean. Next, you'll need to find your pressure switch and test continuity across it. It should be closed with the pump on, open with the pump off. If the system is running properly and the switch doesn't close, take it out and see if you've got any calcium buildup blocking the opening in the bottom of the switch.

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