A Hayward LO code is a limit string open error that occurs when any safety circuits on your Hayward pool heater opens. This forces the heater to shut down and go into lockdown to protect your whole equipment from damage.
The LO code on a Hayward heater means Limit Open, where one of the limit switches is not closing to complete the circuit.
To clear the LO code, fix or replace the wiring on the limit switches and any other issues with your heater’s limit switch, and you may need to do a backwash to clear out any obstructions. Besides that, you’ll need to set the correct water pressure setting. That is if your heater is installed below or above the water levels of your pool or spa.
What Causes the Hayward Heater LO Code?
1. There Is A Fault With The Water Pressure Switch
Chart: Water pressure switch fault possible causes and main fixes.
| FAULTY PRESSURE SWITCH POSSIBLE CAUSE | FIXES |
| PUMP NOT RUNNING | TURN ON THE PUMP |
| LOW WATER FLOW | ENSURE THAT THE WATER FLOW RATE TO THE HEATER IS ABOVE THE MINIMUM THRESHOLD. |
| A FAULTY WIRING OR CONNECTION | ENSURE THAT THE WATER FLOW RATE TO HEATER IS ABOVE THE MINIMUM THRESHOLD. |
| WATER PRESSURE SWITCH CONTACTS OPEN | MEASURE FOR CONTINUITY ACROSS THE WATER PRESSURE SWITCH |
| THERE IS LOW PUMP PRESSURE | CLEAN UP FILTERS OR CLEAR BLOCKAGES |
| INCORRECT WATER PRESSURE SWITCH SETTING | ADJUST WATER PRESSURE SETTING ACCORDINGLY |
| A DEFECTIVE WATER PRESSURE SWITCH | REPLACE WATER PRESSURE SWITCH |
How to diagnose if the water pressure switch has a fault
A faulty water pressure switch is among the most common causes of the LO code on a Hayward heater. You can take the following steps to diagnose a faulty water pressure switch.
I. Verify that the water pump is running
II. Verify also that the water flow rate is above the minimum threshold
III. If the above steps do not show any problems, check for faulty wiring or connection in the pressure switch wiring
IV. Verify the status of water pressure switch contacts
V. Ensure there is no low water pressure from pump
VI. Ensure there is a correct water pressure switch setting
VII. If all the above diagnostic steps look good, ensure the water pressure switch is not defective.
Replacement parts are discussed below:
- Water pressure switch assembly replacement
- Fits hayward millivolt electronic h-series ed1 and ed2 style pool heater
- Weighs 23-pound
- Water pressure switch
- Fits hayward universal h-series low nox pool heater models h150fdn, h150fdp, h200fdn, h200fdp, h250fdn, h250fdp
- Also fits hayward universal h-series low nox pool heater models h300fdn, h300fdp, h350fdn, h350fdp, h400fdn, h400fdp
- Weighs 20 pounds
- Replacement Water Pressure Switch For C Spa Series And H Series Hayward Heaters
- Replacement Pressure Switch For Hayward Above Ground H Series Pool Heater
- Replacement Pressure Switch For Hayward C Spa Series Spa Heaters
- Country Of Origin: United States
LO CODE FIXES
Step 1: Inspecting the Water Pressure Switch Wiring
- Action Taken: I checked the Water Pressure Switch wiring to ensure the connections were secure.
- Reasoning: Loose or disconnected wiring can often cause false alarms in heater systems.
- Result: The wiring was intact, so I moved on to the next step.
Step 2: Testing Water Pressure Switch Continuity
- Action Taken: With the pump running, I detached the wires from the Water Pressure Switch to measure continuity.
- Reasoning: A continuity test helps determine if the switch is functioning correctly.
- Result: The switch showed continuity, ruling it out as the cause of the LO code.
Step 3: Pressure Switch Adjustment (If Required)
- Note: Some heaters might need the Pressure Switch adjusted. I checked the manual to confirm if this was necessary.
- Action Taken: Since the switch showed continuity, there was no need for adjustment in this case.
Step 4: Temperature Limit Switch Wiring Inspection
- Action Taken: I inspected the wiring of the Temperature Limit Switch for any loose connections.
- Reasoning: Faulty wiring here can lead to overheating and trigger the LO code.
- Result: The wiring was secure and well-connected.
Step 5: Continuity Test for Temperature Limit Switches
- Action Taken: I performed a continuity test across the Temperature Limit Switches.
- Reasoning: This test is essential to ensure these switches are operational.
- Result: The switches were functioning properly, eliminating them as the fault source.
Step 6: Vent Pressure Switch Testing (Indoor Installations)
- Action Taken: For indoor units, I would test the Vent Pressure Switch for continuity.
- Reasoning: This step ensures that the switch is operating correctly and the flue isn’t blocked.
- Result: As mentioned, this was an outdoor unit, so this step wasn’t applicable.
Conclusion and Preventive Measures
- Outcome: After thoroughly inspecting and testing the relevant components, it turned out the issue was due to a minor blockage in the water flow, which was swiftly rectified.
- Advice: Regular maintenance and cleaning of the pool system, especially skimmers and pump baskets, are crucial.
- Final Note: For any complex issues or if you’re unsure about any step, it’s always best to consult a professional. Safety is paramount.
That said, we hope that you have found a solution after reading this troubleshooting guide. If not, then you may want to consider a newer heater, I’ve listed a few below:
- The Hayward Universal H-Series 400,000 BTU Natural Gas Heater delivers premium heating performance for years of reliable, long-lasting comfort
- A durable cupro nickel heat exchanger offers exceptional protection against corrosion and premature failure caused by unbalanced water chemistry
- Durable cupro nickel heat exchanger
- Industry-leading hydraulic performance with faster speed-to-heat capability
- The Hayward HeatPro 140,000 BTU Heat Pump quietly and economically maintains ideal water temperature at all times
- Ultra Gold corrosion-resistant evaporator fin offers unparalleled durability, even in harsh coastal environments
Other Hayward Heater Error Codes:
