Interactive diagnostic wizard for Pentair MasterTemp gas heater error codes including ERR IGN, ERR PS, ERR HLS, ERR AGS, ERR AFS, and sensor faults.
Select the symptom or error code your MasterTemp 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 Pentair MasterTemp gas pool and spa heater. 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, component resistance tests, and gas pressure readings. Each symptom card links to a comprehensive written guide when you need to go deeper.
The table below summarizes the most common Pentair MasterTemp error codes and their meanings. Click the troubleshooter above for step-by-step diagnosis of each code.
| Error Code | Description |
|---|---|
| ERR PS | Water Pressure Switch fault — insufficient water flow detected before ignition |
| ERR HLS | High Limit Switch tripped — water temperature near heat exchanger exceeded safe limit |
| ERR AFS | Air Flow Switch fault — combustion air not detected by blower vacuum switch |
| ERR IGN | Ignition Failure — blower runs but no flame detected after 3 ignition attempts |
| ERR AGS | Automatic Gas Shutoff — water exceeded 140°F at second heat exchanger pass |
| ERR SFS | Stack Flue Sensor fault — flue temperature sensor circuit open or out of range |
| E05 | Stack Flue Sensor open circuit — sensor wiring disconnected or thermistor failed open |
| E06 | Stack Flue Sensor short circuit — sensor wiring shorted or thermistor failed shorted |
| E01 | Water Temperature Sensor open circuit — sensor disconnected or failed open |
| 126 | Water Temperature Sensor short circuit — sensor wiring shorted or thermistor failed |
For a complete walkthrough of every error code with photos and wiring diagrams, see the full Pentair MasterTemp troubleshooting guide.
ERR IGN means Ignition Failure. The heater attempted to light three times and was unable to detect a flame. Common causes include a closed gas supply valve, insufficient gas pressure, a fouled igniter, or a clogged burner orifice. Start by verifying the gas supply is on and other gas appliances in your home are working. If the gas is fine, a technician will need to inspect the igniter and gas valve.
ERR PS is the Water Pressure Switch error. The heater's pressure switch did not detect adequate water flow before attempting ignition. The most common causes are a dirty filter, a closed valve in the return line, or a pump that is not running at the required minimum flow. Clean the filter, open all valves, and verify the pump is running before calling a technician.
ERR AGS stands for Automatic Gas Shutoff. This critical safety fault triggers when the water temperature at the second pass through the heat exchanger exceeds 140 degrees Fahrenheit. The front panel buttons are disabled when ERR AGS is active — you must cycle power at the breaker to reset. Common causes include inadequate water flow, severe scale buildup in the heat exchanger, or a bypass valve restricting flow. If ERR AGS recurs, stop operating the heater and call a qualified technician.
ERR HLS is the High Limit Switch error. This safety switch trips when it detects water temperature approaching an unsafe level, usually because of low flow through the heat exchanger. Check that the pump is providing adequate flow, the bypass valve is not diverting too much water away from the heater, and the filter is clean. If the switch trips repeatedly even with good flow, the switch itself or the heat exchanger may need professional inspection.
Short cycling — where the heater fires, runs briefly, then shuts off — is typically caused by insufficient water flow through the heat exchanger. Check that the filter is clean, the pump is running at adequate speed (especially with variable-speed pumps), and the bypass valve is not diverting too much water around the heater. Scale buildup inside the heat exchanger can also cause the temperature rise to be too high, tripping the high limit switch and shutting down the heater.
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 and gas pressure testing 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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