Hayward heater...
LO is simply informing you that the Heater is not sensing proper water flow through it! 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.
Pentair / Sta-Rite heater...
'Lockout' - after 3 attempts of trying to ignite the heater will lockout. Gas Valve will not operate and system is shut down until power cycled off. At this point diagnostics of the heater should be performed.
LO means different things on different brands so please clarify which brand and model. The most common meaning is low flow from the filter system. Try cleaning the filter...or add the requested information please.
SOURCE: Hayward H250 giving me a "LO" error code and does not turn on.
9 times out of ten this means that you have a faulty water pressure switch. It could also be a limit switch, or air pressure switch. Make sure the filter is cleaned, and all valves are in the correct position. Once you are CERTAIN that water is flowing through the heater, you will need to short each individual component to find the faulty one.
SOURCE: "LO" error code on new H400FDN heater
it is low water pressure sensed, unit will not start unless pump is working
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.
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
SOURCE: Hayward H250K gas pool heater error code
Low Flow errors are not necessarily real. They can be caused by improper adjustment or a defect of the pressure switch. Locate the pressure switch. Verify that the "switch" makes contact. Adjust the dial, reducing the distance the switch has to travel to engage. This will effectively lower the operating pressure required to operate. Keep adjusting until the unit stays on.
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