LO (Low Temperature Fault)
Hayward Pool Heater
Severity: ModerateWhat it means
LO on a Hayward heater means the water temperature sensor is reading unusually low or the sensor has failed.
This can happen in very cold weather, with a failed sensor, or when the sensor connection is loose.
Check the temperature sensor and its wiring.
Affected Models
- Hayward Universal H-Series H150
- Hayward H200
- Hayward H250
- Hayward H350
- Hayward H400
Common Causes
- Temperature sensor (thermistor) failed
- Sensor wire disconnected or corroded
- Water temperature actually very cold (below 40°F)
- Sensor in wrong location — not reading pool water
- Control board fault
How to Fix It
-
Check the water temperature with a separate thermometer.
If the pool is actually cold (below 50°F), the LO reading may be accurate.
The heater should still fire — if it does not, the sensor may be out of range. -
Check the temperature sensor wiring.
The sensor plugs into the control board.
Make sure the connector is seated firmly and the wires are not corroded. -
Test the sensor with a multimeter.
The thermistor should read about 10K ohms at 77°F (25°C).
Significantly different readings indicate a failed sensor. -
Replace the temperature sensor.
Hayward temperature sensors cost $15-$30 and are easy to replace.
Frequently Asked Questions
Can I heat my pool in winter?
Gas heaters can heat in any weather.
Heat pumps struggle below 50°F ambient air temperature.
Gas heaters are more effective for cold-weather heating.
How much does it cost to heat a pool?
Gas heater: $200-$600/month depending on size and temperature rise.
Heat pump: $50-$150/month (more efficient but slower).