Pool Heater & Heat Pump Error Codes by Brand
What Every Code Means and When to Call a Pro
Seeing an error code on your pool heat pump? Pick your brand to see every code for your model, or use the chart below to see what the most common codes mean across Hayward, Pentair, AquaCal, AquaComfort, Raypak and Gulfstream.
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Find Your Pool Heater's Error Codes by Brand
Each brand page lists every code for every model, what it means, what to check first, and how urgent it is, plus the official manuals.
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Common Pool Heat Pump Error Codes Across Brands
Different brands use different codes for the same problems. Find your code in the chart to see what kind of problem it is, then open your brand’s page for the exact meaning and fix. Codes ending in 3 or 5 (like HP3 or LP5) mean the problem happened repeatedly and the heat pump locked itself out.
Problem | ||||||
|---|---|---|---|---|---|---|
Low or no water flow | FLo, E03 | LOW WATER FLOW | FLO, LOW | FLO, LOW FLOW, FL3 | FLo, E3, Water PS Open | NO FLOW, WATER FLOW HP, WATER FLOW LOCKOUT |
High refrigerant pressure | HP, E01 | HIGH REFRIG | HP, HP5, HIGH PRESSURE FAULT, AL10, AL11 | HP, HPS, HP3 | HP, HP3, E1, Hi Press Trip | HIGH REFRIGERANT PRESSURE |
Low refrigerant pressure | LP, E02 | LOW REFRIG | LP, LP5, LOW PRESSURE FAULT, AL12, AL13 | LP, LPS, LP3 | LP, LP3, E2, Lo Press Trip | LOW REFRIGERANT PRESSURE |
Defrost cycle | FS | — | FS | FS, DEF, Defrosting | FS | DEFROSTING |
Water too hot | — | HIGH WATER TEMP | OtA, HIGH WATER TEMP, OTA SYSTEM LOCKOUT | High Water Temperature | Outlet Over Temp | MAX WATER TEMPERATURE |
Water temperature sensor | P01, P02 | WATER THERM SHORT / OPEN | pC, pO, WATER TEMP sensor | tSO, tSS, Pc, PO | In / Out Sensor Open or Short | WATER SENSOR MALFUNCTION |
Defrost / coil sensor | P05 | SUCTION TH SHORT / OPEN | dPC, dPO, DEFROST sensor | dPO, ESO, ESS | Coil Sensor Open / Short | EVAP SENSOR MALFUNCTION |
Low or No Water Flow Codes
Flow codes are the most common heat pump error codes. The heat pump’s water pressure or flow switch isn’t sensing enough water, so it won’t run. It’s usually a dirty filter, a pump that’s off or losing prime, or a valve bypassing the heater, not a broken part.
- Make sure the pool pump is on and primed. If it’s a variable-speed pump, run it faster.
- Clean the filter and empty the pump and skimmer baskets.
- Make sure valves aren’t sending water around the heater.
If the code comes back with good flow, the pressure switch may need adjusting or replacing. Schedule a repair or call 407-786-0000.
High Refrigerant Pressure Codes
High pressure codes mean the refrigerant high-pressure switch shut the compressor off to protect it. On a heat pump that’s heating, the most common cause is low water flow, so check flow first. If it keeps tripping, or shows a lockout code like HP3 or HP5, turn it off and call. Running it this way strains the compressor. Schedule a repair or call 407-786-0000.
Low Refrigerant Pressure Codes
Low pressure codes mean the refrigerant low-pressure switch shut the compressor off. Causes include a fan that isn’t running, blocked airflow or a dirty coil, heavy ice, very cold weather, or a refrigerant leak. If it shows on a warm day or keeps coming back, it’s often a leak. Only an EPA 608 certified tech can test and recharge refrigerant, and our techs are certified. Schedule a repair or call 407-786-0000.
Defrost Codes (FS, DEF, Defrosting)
These mean the heat pump paused heating to melt frost off its coil. It restarts on its own once the coil clears. If it stays in defrost, defrosts on mild days, or heavy ice keeps building, the defrost sensor or another part may be failing. Schedule a repair or call 407-786-0000.
Water Too Hot Codes
These mean water coming into the heat pump is hotter than it should be, usually above about 107–110°F. The usual cause is a gas heater or solar system sending hot water straight into it. If nothing else is heating the water, a sensor or control board needs to be checked. Schedule a repair or call 407-786-0000.
Sensor Codes
Sensor codes mean the control board isn’t getting a good reading from a water, coil or air temperature sensor. A power cycle sometimes clears one. If it comes right back, the sensor or its wiring needs to be tested and likely replaced. Schedule a repair or call 407-786-0000.
3 Things to Try Before Calling a Technician
Power-cycle
Turn the heat pump off, then the circuit breaker. Wait 5 minutes and restore power. This clears many lockout codes once the cause is fixed.
Check water flow
Most heat pump codes (flow, and often high pressure) are caused by low water flow, not a broken part. Confirm the pump is on, the filter is clean, and water isn’t being diverted away from the heater.
Check outside temp
Heat pumps slow down, defrost or stop in cold weather. Low pressure and defrost codes can show up when it’s cold. If they keep showing once it warms up, call us.
Disclaimer: This page is for informational purposes only. Heat pumps involve electricity, refrigerant, and moving parts, and internal repairs should always be done by a qualified technician. Improper service may void your warranty or cause injury.
How to Reset a Pool Heat Pump
- Turn the heat pump off at its control.
- Switch off the breaker or disconnect.
- Wait 5 minutes.
- Turn the power back on, then the heat pump.
Some lockouts need a specific button. For example, Gulfstream’s Water Flow Lockout resets by holding the DOWN arrow for 5 seconds. Your brand’s page has the exact steps.
If the code comes back, the reset cleared the message but not the cause. Schedule a repair or call 407-786-0000.
When an Error Code Means You Need a Professional
- Quick checks first: low or no flow codes (pump, filter, baskets and valves), defrost codes, and a keypad lock. If the code comes back, call.
- Call soon: high or low pressure codes that keep returning, sensor codes, water too hot with no other heat source, and display or communication codes.
- Stop unit now: lockout codes (like HP3, HP5, LP3, LP5), compressor and inverter codes, and a breaker that keeps tripping. Turn the unit off before calling.
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Need help? Call us at 407-786-0000 or visit our pool heater repair page to learn more
FAQs
What are the most common pool heat pump error codes?
Low or no water flow codes (like FLO, LOW FLOW, E03 or Water Flow Lockout) are the most common, followed by high and low refrigerant pressure (HP and LP) and defrost codes (FS). Flow and high pressure codes are usually caused by a dirty filter, a pump problem or a valve bypassing the heater. Schedule a repair or call 407-786-0000.
What does FLO mean on a pool heater?
FLO means little or no water is flowing through the heater, so it won’t run. Check that the pool pump is on, the filter is clean, and valves aren’t sending water around the heater. Hayward, AquaCal, AquaComfort and Raypak all use FLO or a similar flow code.
What do HP and LP mean on a pool heat pump?
HP means the refrigerant high-pressure switch opened, usually from low water flow. LP means the low-pressure switch opened, which can mean a fan or airflow problem, very cold weather, or a refrigerant leak. Codes like HP3, HP5, LP3 or LP5 mean it happened repeatedly and the heat pump locked out. Schedule a repair or call 407-786-0000.
Why do heat pump error codes end in 3 or 5?
On many brands, a 3 or 5 at the end of a code means the problem happened that many times in a row and the heat pump locked itself out to prevent damage. AquaComfort and Raypak use 3 (HP3, LP3, FL3), and AquaCal uses 5 (HP5, LP5). A lockout usually needs a power reset after the cause is fixed.
How do I reset my pool heat pump?
Turn it off at the control, switch off the breaker, wait 5 minutes, then turn it back on. That clears most lockouts once the cause is fixed. Some brands have a specific reset, like holding a button, so check your brand’s page.
Can I fix a pool heat pump error code myself?
Some codes clear once you fix the cause, like turning the pool pump back on or cleaning the filter for a flow code. Refrigerant, sensor, compressor and electrical codes need a certified tech. Call 407-786-0000 and we’ll tell you over the phone whether it needs a visit.
Do you repair all heat pump brands?
Yes. Our HVAC and EPA 608 certified techs repair Hayward, Pentair, AquaCal, AquaComfort, Raypak, Gulfstream, Sunrunner and other pool heat pumps, and we ship parts nationwide. Start with free basic troubleshooting by phone.
Is it time for a new pool heater?
If your pool heater is beyond repair, we can help. See our pool heater replacement options to find the right heat pump for your pool.
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