What every pool heater code has in common
A pool heater code almost always names a safety that has opened, not a part that has failed. The heater watches four things: water flow, air flow, flame and temperature. When one goes out of range a switch opens, the heater stops firing, and the display names the switch. So the first question is never which part to buy. It is why the switch opened.
Water flow is the fault you can most often clear yourself, and each maker gives it a message of its own. Go to Pentair, Hayward, Raypak or Jandy for the full list.
| What opened | Pentair MasterTemp | Hayward Universal H-Series | Raypak Digital | Jandy JXi |
|---|---|---|---|---|
| Water flow | ERR PS | LO | Water Sw Open | CHECK FLOW |
| Air or vent | ERR AFS | AO, LO | Vent/Field Sw #1 | 1 flash of the ignition LED |
| Flame | ERR IGN | IF, IO, HF | Ignition Lockout | FAULT- CHECK IGN CONTROL |
| Water too hot | ERR HLS, ERR AGS | HS, LO | Hi Limit 1 is open | FAULT- HIGH LIMIT |
| Water sensor | E01, 126 | SF | Sensor Failure | FAULT- OPEN WATER SENSOR |
Pool heater not heating: what to check first
- Write the code down exactly. On a MasterTemp, ERR HLS and ERR AGS are separate safeties that open at 135F and 140F.
- Water. Pump running, filter clean, every valve between the pump and the heater open. Jandy lists a variable speed pump set too low among the causes of CHECK FLOW, so check the speed too.
- Air. From outside the cabinet, clear leaves and debris from the vent and the air openings.
- Gas. Confirm the manual shutoff on the pipe outside the heater is open. Your gas check ends there.
- Reset once. ERR PS clears by itself when flow returns, ERR IGN with the HEATER OFF button, ERR AGS by cycling the power. A Hayward showing IF retries without you.
- Same code again? Stop. Go to when to stop.
Pentair MasterTemp error codes
Pentair has built the MasterTemp with two front panels. A display that spells out ERR and two or three letters is the current heater. Two lights marked SERVICE SYSTEM and SERVICE HEATER mean the older one. Go by the panel, not by the heater's age.
Current MasterTemp: codes on the display
These come from Table 8 of Pentair's MasterTemp installation and user's guide, part number 472592, Rev. Q, dated 7/30/23. That manual covers the MasterTemp 400 with the smaller sizes, so the 400 has no list of its own.
| Code | What the manual says it means | What to check |
|---|---|---|
| ERR PS | Water pressure switch open: too little water is moving through the heater. Clears by itself when flow returns | Pump, filter, valves. Nothing to reset |
| ERR HLS | High limit switch open: water off the heat exchanger's first pass is hotter than 135F | Confirm full flow, let it cool, try once |
| ERR AFS | Air flow switch open: the blower is off or its air is restricted. Uncorrected after 60 seconds, the heater has to be switched off | Clear debris from the air path. A dead blower is a technician's repair |
| ERR IGN | The ignition control module could not light the heater. HEATER OFF clears it | Gas shutoff open. Press HEATER OFF, call for heat once |
| ERR AGS | Automatic gas shutoff open: water leaving the second pass is hotter than 140F. Resets only by cycling the power | Confirm full flow, cycle the power once |
| ERR SFS | Stack flue too hot, over 480F | Heater off. Call a technician |
| E05, E06 | Stack flue sensor open (E05) or shorted (E06) | The sensor and its wiring |
| E01, 126 | Water temperature sensor open (E01) or shorted (126) | The thermistor and its wiring |
Older MasterTemp: indicator lights
The older panel is in Rev. M of the same guide, dated 1/2015. It shows no codes, only 2 lights and 6 diagnostic LEDs.
| Light | What the manual says it means | What to check |
|---|---|---|
| SERVICE SYSTEM | Too little water is reaching the heater | Pump, filter, valves, as for ERR PS |
| SERVICE HEATER | The fault is in the heater or its controls | Note which diagnostic LED is lit |
| Diagnostic LEDs | Six, marked AGS, AFS, HLS, PS, THERMISTOR and SFS | Five share their letters with the codes above. Rev. M says what each means on your heater |
Replace a part only when the code names it and the simple causes are ruled out. ERR PS with full flow proven leaves the MasterTemp water pressure switch. ERR HLS that returns with full flow and pool water nowhere near 135F leaves the high limit switch. E01 and 126 name the water temperature sensor, which is the thermistor for the MasterTemp and Max-E-Therm. E05 and E06 name the stack flue sensor, and this replacement stack flue sensor is made for both heaters.
Two codes do not mean the part in their name has failed. ERR AFS opens because air is short, so it points at the blower and the air path, and a new switch fixes neither. ERR IGN says only that the module could not light the heater, not why. If a technician traces it to the module itself, this is the ignition control module kit for the MasterTemp.
Every MasterTemp part we carry is under Pentair MasterTemp heater parts.
Hayward Universal H-Series error codes
Hayward uses two letters. These come from its consumer troubleshooting guide for the Universal H-Series, document CTSG-UHS16b, 2017, which covers the FD models on natural gas and propane, ASME versions included.
| Code | What the manual says it means | What to check |
|---|---|---|
| LO | One of 3 switches has faulted: water pressure, vent pressure or temperature limit | Water first: pump, filter, valves. Then the vent |
| IF | Ignition failure. The heater tries 3 times, locks out, waits 60 minutes, then tries 3 more | Gas shutoff open, vent clear. Let it retry |
| HS | Return water passed its maximum temperature, or heated too fast, or both | Confirm full flow, try once |
| AO, AC | Blower vacuum switch open (AO) or closed (AC) | Vent and air openings clear |
| IO | Ignitor circuit open | The ignitor and its wiring |
| HF | Flame is present while the gas valve has no power | Heater off, gas shutoff closed, call a technician |
| SF | The temperature sensor input, a thermistor, has failed | The thermistor and its wiring |
| PF | Low voltage, or polarity reversed | The supply, by an electrician |
Four more are the electronics. BD and EE are a bad board, BD also a secondary high voltage fault. CE is lost communication between control module and display. SB is a failed keypad.
LO is the one people misread. It is not a low temperature reading, and nothing in its meaning mentions gas. It is 3 switches, so it points at 3 parts. With flow proven, the water side is the H-Series pressure switch and the temperature side is the high limit kit. The vent pressure switch is the third, and a technician tests it.
AO names the blower vacuum switch, once the vent is clear. SF names the FD thermistor. EE and BD name the FD control board kit. IO names the ignitor: take its number from the parts list in your manual, and check the others against it too.
LP is not LO. It belongs to Hayward's older HeatPro and Summit heat pumps, where Hayward's 2012 heat pump guide ties it to air that stays below 21F, clearing once the air passes 40F.
Every H-Series part we carry is under Hayward H-Series heater parts.
Raypak Digital error codes
Raypak writes its faults out in words. These are from Tables P and Q of Raypak's Digital installation and operation manual for the 206A, 266A, 336A and 406A, part number 241236, Rev. 50, effective 08-24-26.
| Code | What the manual says it means | What to check |
|---|---|---|
| Water Sw Open | Water pressure switch open | Pump, filter, valves |
| Hi Limit 1 is open, Hi Limit 2 is open | The high limit it names has opened. ASME units alone make it a manual reset, which the MODE button clears | Confirm full flow, let it cool. ASME: press MODE once |
| Rollout Sw Open | Flame rollout switch open | Heater off, gas shutoff closed, call a technician |
| Ignition Lockout | With No pilot sensed: no pilot flame in the time allowed, 15 or 90 seconds. With Main Ign Failure: the pilot went out in the 8 second trial for the main burner | Gas shutoff open. Reset once |
| Sensor Failure, Sensor Open, Sensor Short | Failure: the 2 thermistors read more than 2F apart. Open or Short: one has failed that way | The sensor and its wiring |
| Clock/Fireman Sw | An open circuit at the time clock or the fireman switch | The clock or controller, not the heater |
| Vent/Field Sw #1 | Vent spill switch open, or field switch 1 | Vent clear of debris |
| Low Temp Lockout | Water colder than 36F | Nothing has failed |
Three more are beyond a homeowner's check. Flow/Field SW #2 is a flow switch the installer supplied, or a second field switch. Flame w/o CFH is flame sensed with the pilot valve and the main valve both ordered shut: close the gas and call. Internal Fault is the board.
The high limit messages name their own parts, the High Limit 1 kit and the High Limit 2 kit. Match each number to the illustrated parts list in your manual first, and do the same for a pressure switch or a sensor.
Every Raypak Digital part we carry is under Raypak Digital heater parts.
Jandy JXi fault messages
These are from sections 10.2 and 10.3 of Jandy's JXi installation and operation manual, document H0574300, Rev M. People quote a message as Fault-Check Igniter. Rev M does not print those words. It prints FAULT- CHECK IGN CONTROL, the closest message it has. Older Jandy heaters were not checked.
| Code | What the manual says it means | What to check |
|---|---|---|
| CHECK FLOW | 4 causes listed: pump off, pump pressure low, pressure switch faulted, variable speed pump set too slow | Pump on and fast enough, filter, valves |
| FAULT- HIGH LIMIT | Water in the heater is past the internal limit, or a limit switch has faulted | Confirm full flow, let it cool, try once |
| FAULT - HIGH FLUE TEMPERATURE | The flue temperature limit has faulted | Heater off. Call a technician |
| FAULT- CHECK IGN CONTROL | 6 causes listed: damaged tubing on the air pressure switch, a stopped or slow fan, restricted air, a broken igniter, gas supply short on pressure or volume, a burner with no flame | Vent clear, gas shutoff open. The rest is a technician's |
| FAULT- OPEN WATER SENSOR, FAULT- SHORTED H2O SENSOR | The water temperature sensor has failed, or its wiring is faulty | The sensor and its wiring |
| FAULT- PUMP | A status, not a fault. The heater is in Maintain Temp mode with the filter pump switched off. No service needed | Nothing |
| Ignition control LED | 1 flash: air flow fault. 2: flame with no call for heat. 3: lockout after 3 failed tries to fire. Steady: ignition control fault | Count the flashes for the technician |
Two of those listed causes are parts. CHECK FLOW with the pump proven leaves the JXi pressure switch and siphon loop. A broken igniter means the JXi igniter kit, which fits the 200, 260 and 400. It is 1 cause of 6, so have it confirmed before you buy.
Every JXi part we carry is under Jandy JXi heater parts.
When to stop and call a technician
Never jumper a switch or a sensor, and never bypass the switch that tripped, not even as a test. A pool heater burns gas, and a heater that fires with a safety defeated proves only that the safety was right.
Turn the heater off and close the gas shutoff for any code that reports flame or heat where none should be: HF on a Hayward, Rollout Sw Open and Flame w/o CFH on a Raypak, 2 flashes or a high flue temperature fault on a Jandy, ERR SFS on a Pentair. For everything else, stop after 1 reset.
Fuel conversion is the job all four manuals take out of your hands. Pentair says never to run a natural gas heater on propane or the reverse, and to hand any conversion to a qualified technician who uses factory approved parts. Hayward and Raypak limit it to a qualified agency. Jandy advises against converting a JXi at all, and wants a licensed professional if it must happen.
Before the cabinet comes open, know four things:
- The rating plate names the gas. A heater burns the one gas printed there.
- Gas pressure is a measurement, not something you can see. Raypak wants 6 to 10.5 in. WC on natural gas and 12 to 13 on propane. Pentair wants 4 to 14 on the MasterTemp, dropping no more than 2 inches from static to running. Raypak calls undersized gas pipe one of the most common faults in a replacement.
- The exhaust may be under pressure. The MasterTemp's is, so it must never wear a drafthood, and it needs Pentair's vent conversion kit indoors. A JXi needs exhaust conversion kit R0731100 before it is vented indoors.
- Indoors, fit carbon monoxide detectors. Pentair and Jandy both strongly recommend them by the heater and in the occupied rooms beside it.
When the code does name a part, shop pool heater parts by its number.