Interactive diagnostic wizard for Hayward Universal H-Series gas heater error codes including PF, IF, LO, AO, AC, HS, SF, HF, bD, EE, and CE codes.
Select the symptom or error code your H-Series heater is displaying to get step-by-step troubleshooting guidance.
Click a symptom or error code to see diagnostic steps.
This interactive troubleshooting wizard is designed specifically for the Hayward Universal H-Series gas pool and spa heater (models H150FD, H200FD, H250FD, H300FD, H350FD, H400FD, and propane variants). Whether you are a pool homeowner trying to decode an error code on your heater display or a service technician running a structured diagnostic, the wizard adapts to your role and provides the appropriate level of guidance.
Select the "Homeowner" role for safe, practical checks you can perform yourself, or switch to "Technician" mode for detailed diagnostic procedures including voltage measurements, gas pressure readings, thermistor resistance tests, and vacuum switch diagnostics. Each symptom card links to a comprehensive written guide when you need to go deeper.
The table below summarizes the most common Hayward Universal H-Series error codes and their meanings. Click the troubleshooter above for step-by-step diagnosis of each code.
| Error Code | Description |
|---|---|
| PF | Power Fault — supply voltage polarity reversed or voltage too low |
| IF / IO | Ignition Failure — heater clicks and blower runs but never lights after multiple attempts |
| LO | Water Pressure — safety string open due to pressure switch, limit switch, or vent issue |
| AO | Blower Vacuum Switch closed when it should be open (blower off) |
| AC | Blower Vacuum Switch open when it should be closed (blower on) |
| HS | High Temperature — high return water temperature or rapid temperature rise detected |
| SF | Sensor Failure — temperature sensor (thermistor) input out of range |
| HF | Flame Sensed with Gas Valve Off — SERIOUS SAFETY ISSUE requiring immediate gas shutoff |
| bD | Board Communication Error — control board internal fault |
| EE | EEPROM Error — control board memory fault |
| CE | Communication Error — display board and main board cannot communicate |
For a complete walkthrough of every error code with photos and wiring diagrams, see the full Hayward Universal H-Series troubleshooting guide.
IF and IO both indicate Ignition Failure. The heater attempted to light multiple times and was unable to detect a flame. Common causes include a closed gas supply valve, insufficient gas pressure, a worn igniter that does not glow bright orange, or a dirty flame sensor. Start by verifying the gas supply is on and other gas appliances are working. After 3 failed attempts, the heater locks out and must be power-cycled to reset.
LO is the Water Pressure code. The heater's pressure switch did not detect adequate water flow. The most common causes are a dirty filter, a closed valve near the heater, or a pump that is not running at the required minimum flow rate. H150 and H200 models need 25+ GPM, while H250 through H400 need 40+ GPM. Clean the filter, open all valves, and close any bypass valve that may be diverting water around the heater.
HF is a serious safety code meaning the flame sensor is detecting flame when the gas valve should be closed. This can indicate a stuck-open gas valve or a leaking gas valve diaphragm. You should immediately shut off the gas supply to the heater and NOT attempt to restart it. Only a licensed technician should diagnose and repair this issue. The gas valve assembly will typically need to be replaced.
HS is the High Temperature code. It triggers when the heater detects a high return water temperature or rapid temperature rise, which can indicate insufficient water flow through the heat exchanger. Let the heater cool for 15 minutes, verify the pump is providing adequate flow, and check for scale buildup inside the heat exchanger. If using with a spa, make sure the desired temperature is not set too high.
AO and AC are both related to the blower vacuum switch. AO means the vacuum switch is closed when it should be open (with the blower off), while AC means the switch is open when it should be closed (with the blower running). Common causes include a blocked exhaust vent (leaves, bird nests, ice), a clogged condensation drain, a cracked vacuum hose between the blower housing and the switch, or a failing blower motor.
Yes. Select the "Homeowner" role and the wizard will show only the checks that are safe and practical for a non-professional to perform. Technician-level steps such as voltage measurements, gas pressure testing, and thermistor resistance checks are hidden unless you switch to Technician mode. Always follow the safety warnings on screen, and consult a licensed pool service professional for any repair you are not comfortable performing.
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