Q: I went to turn on my pool heater, which is a Hayward model, but it flashes the LO code as seen in the image below. Can you help me fix this?
According to the Hayward Heater Manuel: The Hayward heater LO code indicates a fault in the temperature limit switch, vent pressure switch, or water pressure switch. To fix it, ensure the pump is on, is wired and connected well, the water flow is above the required minimum pressure, and the filters are clean. Replace defective switches.
A: Would be glad to answer as I have worked on Hayward pool heaters for years and the LO code is one of the most common. This code is a ‘limit string open error,’ indicating that the limit string is open, causing your heater to shut down and go into lockout. Don’t worry, I’ll guide you through some steps to fix this. Remember, if you correct the error and the limit string closes, the heater should automatically restart within 2 minutes.
- 1. Check the Pump: First, ensure that your pump is on. The LO code often appears when the pump isn’t running or isn’t providing enough water flow. The pump needs to be wired and connected properly for optimal performance.
- 2. Water Flow: Your heater requires a certain minimum water pressure to operate correctly which is 20 GPM (H150FD & H200FD), 25 GPM (H250FD & H300FD), and 30 GPM (H350FD & H400FD).. If the water flow is too low, it can trigger the LO code. Check if the water flow is above the required minimum pressure. This can often be a simple fix.
- 3. Clean Filters: Dirty filters can restrict water flow, leading to the LO code. Make sure your filters are clean. Regular cleaning and maintenance of filters can prevent many common heater issues.
- 4. Switches Inspection: The LO code can also indicate a fault in the temperature limit switch, vent pressure switch, or water pressure switch. These switches are crucial for the safe operation of your heater. If any of these switches are defective, they need to be replaced.
- 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
- Water pressure switch assembly replacement
- Fits hayward millivolt electronic h-series ed1 and ed2 style pool heater
- Weighs 23-pound
Other reasons for the Hayward heater LO code
Hayward pool heater troubleshooting should be done only when you have the proper knowledge of the pool heater. Otherwise, it’s advisable just to enlist the services of a professional since you risk damaging the pool heater.
Other issues, including the following, cause the LO code:
| LO code fault | Main fixes |
| Faulty water temperature switch | Turn on the water pump, ensure adequate flow and connections, clean filters, replace the water temperature switch if needed. |
| Faulty temperature limit switch | Ensure adequate flow, proper connection, replace the temperature limit switch if needed. |
| Faulty vent pressure switch | Ensure adequate flow and proper connection, and replace the vent pressure switch if needed. |
- Item Package Weight: 4.9 lb
- Country Of Origin: United States
- Temperature limiters kit replacement
- Package Dimensions: 14.223 L x 0.762H x10.16W (centimeters)
Time for a new pool heater?
If you can’t implement any of these remedies, you should consider calling for an expert to fix it for you. This helps prevent further damage to the pool heater which may cost you even more to fix.
With these steps, you should be able to restore the correct workings of your Hayward pool heater by doing away with the LO code. While the LO code isn’t something to worry too much about, you should consult with an expert if the fixes above don’t work for your pool heater.
Have a question about pool heaters? Airlucent owner Tim David would like to answer your question in an upcoming article, call (256) 399-9708 or contact David via the contact page.
Other Hayward Heater Error Code Fix Guides:
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.