Interactive diagnostic wizard for Pentair UltraTemp heat pump alarm codes including HIGH REFRIG, LOW REFRIG, LOW WATER FLOW, BROWNOUT, LOW AMBIENT TEMP, and thermistor faults.
Select the symptom or alarm code your UltraTemp is displaying to get step-by-step troubleshooting guidance.
Click a symptom or alarm code to see diagnostic steps.
This interactive troubleshooting wizard is designed specifically for the Pentair UltraTemp heat pump for pools and spas. Whether you are a pool owner trying to decode an alarm message on your control panel 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 pressure switch testing, thermistor resistance measurements, refrigerant system checks, and electrical troubleshooting. Each symptom card links to a comprehensive written guide when you need to go deeper.
The table below summarizes the most common Pentair UltraTemp alarm codes and their meanings. Click the troubleshooter above for step-by-step diagnosis of each alarm.
| Alarm Code | Description |
|---|---|
| HIGH WATER TEMP | Water temperature above 108°F (42.2°C) — bad thermistor or control board fault |
| LOW WATER FLOW | Water pressure switch is open — pump not running, dirty filter, or bad pressure switch |
| HIGH REFRIG | Refrigerant high pressure switch is open — restricted water flow, overcharge, or TXV fault |
| LOW REFRIG | Refrigerant low pressure switch is open — leak, low ambient temp, or faulty fan |
| LOW AMBIENT TEMP | Air temperature too low for heat pump operation — defrost cycle did not complete |
| BROWNOUT | 24 VAC supply voltage to control board is low — bad transformer or insufficient supply voltage |
| WATER THERM SHORT/OPEN | Water temperature thermistor circuit is shorted or open — bad thermistor or control board |
| SUCTION TH SHORT/OPEN | Defrost refrigerant thermistor circuit is shorted or open — bad thermistor or control board |
| FIVE ALARMS | Five faults have occurred within one hour — auto-resets after one hour or manual reset via ON/OFF |
| REMOTE POOL SPA | Pool and Spa remote relay inputs are simultaneously energized — automation wiring conflict |
For a complete walkthrough of every alarm code with diagrams and resistance charts, see the full Pentair UltraTemp troubleshooting guide.
HIGH REFRIG means the refrigerant high pressure switch has opened. This typically indicates insufficient water flow through the heat exchanger, causing the refrigerant system to build excessive pressure. Common causes include a dirty pool filter, a closed bypass valve, the water pump not running, a clogged heat exchanger, or the unit being plumbed backwards. In some cases, the unit may be overcharged with refrigerant. Start by verifying the pump is running and the filter is clean. If the alarm persists, a technician should check the TXV, refrigerant charge, and thermal protector.
LOW REFRIG indicates the refrigerant low pressure switch has opened. This can be caused by a refrigerant leak in the system, air and water temperatures that are too cold for heat pump operation, a faulty fan motor or capacitor, a stuck-closed TXV (thermostatic expansion valve), or insufficient airflow through the evaporator coil due to debris or obstructions. If temperatures are cold, wait for warmer conditions. Otherwise, a technician should check for leaks, inspect the fan, and evaluate the TXV.
LOW AMBIENT TEMP means the refrigerant temperature sensor has detected that the air temperature is too low for heat pump operation, or the defrost cycle did not complete within the allotted 15 minutes. When ice builds up on the evaporator coil and cannot be cleared by the defrost cycle, the unit shuts down with this alarm. Wait for the ice to melt naturally and for air temperatures to rise before restarting. If the alarm appears on a warm day, the defrost thermistor may be faulty and should be tested with a 10k ohm resistance check.
FIVE ALARMS means that five faults of any kind have occurred within a one-hour period. The unit will automatically reset after one hour, or you can manually reset it by pressing the ON/OFF button. This alarm is a symptom of a recurring underlying problem. After resetting, monitor the heat pump to see which specific alarm triggered the five-alarm lockout. That underlying alarm is what needs to be diagnosed and repaired. Common culprits include LOW WATER FLOW from a dirty filter, HIGH REFRIG from restricted flow, or LOW REFRIG from a refrigerant leak.
Ice formation on the outer air coil is normal in cool or humid conditions and is typically handled by the UltraTemp's defrost cycle. However, excessive ice buildup can indicate several problems: the defrost feature may be disabled in the service menu, the discharge airflow may be restricted by nearby plants or structures, sprinklers may be spraying on the coil, or the unit may have a refrigerant leak causing low pressure. Ensure the heat pump has proper installation clearances, enable the defrost feature, and keep vegetation trimmed away. If ice persists, shut off the heater and allow the ice to thaw before restarting.
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 refrigerant pressure readings, thermistor resistance measurements, and electrical component testing are hidden unless you switch to Technician mode. Always follow the safety warnings on screen, and consult a licensed pool service professional or HVAC technician for any repair you are not comfortable performing. Heat pumps contain pressurized refrigerant and high-voltage components that require trained personnel.
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