Hayward Heater LO Code [5 Easy Fixes]

The LO error code means that the limit string is open. The reason why the limit string opens is a low water flow rate.

So, basically, the LO code means that your heater doesn’t have sufficient water flow.

When this occurs you may mistake it as your Hayward pool heater not turning on. But actually, the heater does turn on and gets power but enters a lockout mode that stops the heater from responding.

We will now take an in-depth look at what causes your heater to display LO error code. We will give you easy solutions.

1. Dirty Pool Filter

The number one cause of low water pressure is a dirty and clogged pool filter. If you get this error code, chances are your heater has nothing wrong with it except a dirty filter which is easily solvable.

Solution:

Your filter is either a sand filter, DE filter, or cartridge filter. In my experience, sand filters and DE filters are the most common. Cleaning a cartridge filter is relatively harder.

To clean your DE filter you need to open it up and take out the elements from the tube. Typically, your filter should have 4 elements.

With your garden hose, wash all the dirt and debris you can out of them. In case the elements are too worn out to be reused, replace them and put the filter back together. In case you have a sand filter, follow the instructions below to backwash it.

Turn off the water supply. Close the suction and return lines’ valves. Take off the pump’s cover to clear the filter basket.
Replace the lid if necessary. Open the drain outlet’s valve. Switch the lever to the BACKWASH position. The valve of the return and suction lines need to be open.
Turn on the pump. Rinse for 1 to 2 minutes, or until the fluid in the sight glass is clear. Any electric heaters must be turned off. Turn off the water supply.

Slide the lever to the RINSE position, start the pump, and rinse for 15-30 seconds. Set the lever to FILTER to stop the pump. This is the standard working position.
Now, run the pump after shutting down the drain outlet valve. Turn on the heater.

2. Water Pressure Switch Fault

Another cause for the Hayward pool heater LO failure code appearing on your screen is a water pressure switch fault.

Solution:

Here are the steps you should take to fix this issue and clear the error code.

Step 1: Ensure that the pump is running. The LO code will appear each time the pump is off as without the pump there is no flow. As soon as the pump is on the error code should clear. If not, jump to the next step.

Step 2: Now it’s time to ensure an adequate water flow rate. The required water rates for different models are given below:

Model	Required Water Flow Rate
H150FD/H200FD	20 GPM
H250FD/H300FD	25 GPM
H350FD/H400FD	30 GPM

Step 3: Ensure that the wire harness terminals on the water pressure switch are properly connected to the spade terminals.

Step 4: Remove the wire leads from the water pressure switch and check for continuity across the switch while the pump is running.

The LO code is not caused by a water pressure switch fault if it is closed. Reattach the wires to the water pressure switch.

Step 5: Clean the filter or remove any obstructions. Examine the position of the valves in the plumbing system.

Set the water pressure switch to the desired setting. If the Hayward pool heater LO code persists, the water pressure switch must be replaced.

3. Vent Pressure Switch Fault

The vent pressure switch fault is another cause of the Hayward heater LO code occurring.

Solution:

Here’s how to fix Hayward pool heater error code LO when it is being caused by a vent pressure switch fault:

Step 1: Examine the wiring of the vent pressure switch. Ensure that the wire harness terminals on the vent pressure switch are properly connected to the spade terminals. If everything seems good, move on to step 2.

Step 2: Remove the wires and jumper leads from the vent pressure switch. Operate heater. Measure continuity across the vent pressure switch.

The LO code is not produced by a problem in the vent pressure switch if it is closed. Disconnect the wire leads from the jumper and reattach them to the vent pressure switch.

Step 3: Ascertain that the flue is neither obstructed or restricted. In the installation instructions, look up the criteria for interior vent sizing. If everything seems good, move on to step 4.

Step 4: Replace the pressure switch on the vent.

4. Temperature Limit Switch Fault

Hayward gas pool heater LO code can also be caused by a temperature limit switch fault.

Solution:

Take the following steps to get rid of the error code.

Step 1: Examine the wiring of the temperature limit switch. Ensure that wire harness terminals on temperature limit switches are properly secured to spade terminals. If everything seems good, move on to step 2.

Step 2: Remove the limit switch and jumper leads’ wires. Operate the heater. Measure consistency between limit switches.

The LO code is not caused by a temperature limit switch fault if it is closed. Reconnect the leads to the temperature limits after removing the jumper.

Step 3: Check that the water flow rate to the heater is more than the minimum required. If everything appears to be in order, replace the temperature limit switch.

5. Exhaust Gas Temperature Limit Fault

The last thing you can check when the LO code occurs is the exhaust gas temperature limit.

Continuing to operate the heater after the limit has been reached will result in damage to the complete device, which is not covered by the warranty.

Solution:

Follow the instructions below to get rid of the error code.

Step 1: Make that the wire harness terminals on the temperature limit switch in the flue collector panel above the center of the header are properly attached to spade terminals.

Step 2: Remove the wire leads from the limit switch and check for continuity between the contacts. The LO code is not triggered by a malfunction in the exhaust gas temperature limit switch if it is closed.

Step 3: Low water flow, poor water chemistry, or a combination of these and other conditions may cause damage to the heat exchanger.

Replace the heat exchanger and the exhaust gas temperature limit after resolving any issues with water flow through the heater and water chemistry.

FAQs:

How do you adjust the pressure switch on a Hayward pool heater?

Turn the pressure switch’s adjustment knob clockwise until the heater turns off, then 1/4 turn counter-clockwise until the heater turns back on. The pressure required to close the switch increases as the adjustment knob is turned clockwise.

Where is the pressure switch on a Hayward pool heater?

It is on the side behind the panel on most Hayward pool heater models. The pressure switch keeps track of the water flow rate in your heater.

What does Flo mean on a pool heater?

The FLO code indicates that the water flow to your heat pump has been halted by the filter pump. This error will turn off the heater until the filter pump timer is reset, providing the heat pump with the necessary water flow.

Why does my pool heater say HP?

The high-pressure switch is open if HP or HI is displayed. When the refrigerant pressure exceeds 590 PSI, the switch opens and immediately resets to 440 PSI. Restricted water flow is the most prevalent cause of HP or HI error codes.

How do I know if my flow switch is bad?

A defective flow switch is indicated by a “No Flow” sign going on while the pump is working and water is really flowing through the pipe. The flow switch needs a replacement.

Conclusion

Getting rid of the Hayward heater LO code usually only takes backwashing the filter. The other faults are rare. It’s better if you clean your filter regularly as part of the maintenance of your heater.

In case you are facing any issues with your Hayward pool heater, leave us a comment.

Note: You can also read how to fix Pentair pool heater error codes E01.

Hayward Heater LO Code [5 Easy Fixes]

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