Question about Hayward H-series Electronic Gas Pool Heater H400

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My pool heater flashes LO and BO. - Hayward H-series Electronic Gas Pool Heater H400

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  • Hayward Master
  • 1,631 Answers

"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
BO Message...
This means "By-Passed Operation"
This mode is for systems with 'Automation' controls. If you don't have an automation system, then your heater has a control dip switch or logic jumper that needs to be undone. But if you have automation, do Nothing, your automated system has control of your heater. Good Luck - hope this helped.

Posted on May 25, 2015

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Posted on Jan 02, 2017

  • 5 Answers

SOURCE: Error code LO

Is the heater installed indoors?? if so you'll need a vent pressure orifice kit.
if not check your water press. (below 18 PSI on filter) Place filter on "recir" if it fires and stays on . it's the pressure.
check to see if all connections a set tight hi-ltd switch wire harness etc.

Posted on Jun 07, 2009

  • 139 Answers

SOURCE: hayward pool heater c4205 has error message of LO

lo usually indicates insufficient water flow and/or pressure switch malfunction.make sure filter is clean and pressure is in normal range

Posted on Jun 21, 2009

  • 128 Answers

SOURCE: same problem pool heater shows hayward pool heater bo error

BO means that you have bypassed operations. ie automation. if no automation is present then press and hold the Down arrow and Mode button for 3 seconds.

Posted on Aug 23, 2009

  • 246 Answers

SOURCE: my pool and spa heater is not working diplays

MAKE SURE THE FILTER IS CLEAN THAN THE TEMPETURE SENSOR MAY BE BAD, CLEAN THE FILTER FIRST

Posted on Oct 13, 2009

  • 4 Answers

SOURCE: my hayward heater gives a LO error when trying to

One of your limits is not working or not wired up. An easy way to check the limits - Water pressure switch, Hi limits, air pressure switch all of which have 2 wires going to them. Unplug one item and connect the 2 wires together ( paper clip works fine ) Then retest, if problem does not go away remove paper clip and reconnect wires and move to the next limit. The limits are located in the black plastic header. Always make sure water is flowing through the heater at all times while checking the limits.

Posted on Mar 01, 2010

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