Question about Hayward H Series Pool & Spa Heater 400k Btu Propane Gas Milivolt Ignition H400p1

3 Answers

Hayward H400 heater problem

The heater won't turn on and there is a flashing LO indicator with the service light lit!

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  • Anonymous Apr 25, 2009

    I have the exact same problem. Help!

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LO usually indicates low water pressure. Check the pressure in your filter. You may need to backwash. If the filter is to clogged then the water pressure in the heater is so low that it won't activate the pressure switch. While checking the pressure turn the pump off and then on to make sure the pressure gauge is actually working. Also check the pressure coming out of the inlets into the pool. You should be able to tell if you have sufficient water pressure.

Posted on Jan 28, 2009

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I changed the mimiset &thermostate&pilot&pressure switch
the heater working about 30days and stop after that .
-pls.what is the proplem.
thanks

Posted on Dec 19, 2012

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Depending on your model- you may have to reset it after fixing it. I backwashed mine, had the same LO error code. I pushed "mode" through all the cycles (spa, pool, etc. then back to pool) and it started right up. (I hadn't noticed it but it told me to on the heater below where it told me the various error codes...referred to it as "lock out"). Saved a service call.

Posted on May 10, 2009

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1 Answer

I have a hayward h400ed2 heater and when turned on to heat the temperature can only be increased or decreased in incriments of 10 to 15 degrees. I also used to get a reading of Lo. It didnt happen all the...


already answered your earlier post. the code LO signifies that there isnt enough water flow to allow the heater to run. as for the temp, i wouldnt worry about the display. it will never exceed factory setting. sounds like a stuck button

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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:
  • enough water in pool or spa?
  • 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?
  • Etc
Good Luck - hope this helped.

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I looked up the owners manual for the Hayward H400 heater and it did not list the "ob" indication. For this reason I would call the and they likely can help you out.

Please let me know how this turns out. Thank you.

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