Hayward pool heater error codes

A Hayward heater shows a code when one of its safety checks has failed. The code tells you which check failed, which is where diagnosis starts. On its own it doesn't tell you which part to replace.

This page covers two Hayward troubleshooting guides:

• Universal H-Series gas heaters (models HxxxFD, natural gas and propane): Universal H Series Heaters Troubleshooting Guide, TSG-UHS16b (2017).
• HeatPro and Summit-platform heat pumps: Hayward/Summit Heat Pump Troubleshooting Guide, TSG-HTPMPa (2018). It covers round HeatPro units HP20654T, HP20654BT, HP20654TC, HP20854T, HP20854BT, HP20854TC, HP21104T and HP21104TC, and square units SUM25TA, SUM3TA, SUM3TAC, SUM4TA, SUM4TAC, SUM5TA, SUM5TAC, SUM8TA, HML50TA, HML65TA, HML65TAC, HML80TA, HML80TAC and HML110TA (heat pump guide, p. 4).

Page numbers are the printed page numbers in each guide. Both guides are written for service technicians, and both open with a high-voltage warning that only qualified technicians should work inside the unit (H-Series guide, p. 2; heat pump guide, p. 2). The checks marked as safe below are all done from outside the cabinet.

If you smell gas, leave the area and call your gas utility from a safe place before anything else. Don't light any appliance, don't touch electrical switches, and don't use a phone inside the building. That is the standard instruction printed in gas pool heater manuals, for example Pentair's MasterTemp manual, p. 42.

Universal H-Series gas heater codes

Code	What Hayward says it means	Usually points to (per Hayward's chart)	Safe to check yourself?	Guide page
LO	Limit open: water pressure switch, vent pressure switch or temperature limit switch	Water flow first; normal when the pump is off	Yes: pump, baskets, filter, valves	p. 19; pp. 46-51
IF	Ignition failure: burner didn't light after three tries	Gas supply off, then gas pressure, flame sensor, burners	Partly: whether gas is reaching the house	p. 19; pp. 52-55
HS	Water temperature above 105°F, or a rise of more than 6°F within 60 seconds	Inlet and outlet plumbed in reverse; temperature sensor	No	p. 19; pp. 40-41
SF	Temperature sensor (thermistor) reading out of range	Thermistor, then control board	No	p. 19; pp. 40-41
AO	Blower vacuum switch open when it should be closed	Blower, switch wiring, vacuum tube, voltage selector plug	No	p. 19; pp. 58-60
AC	Blower vacuum switch closed when it should be open	Blower vacuum switch, then control board	No	p. 19; pp. 56-57
IO	Ignitor circuit open	Ignitor wiring and plug, ignitor, control board	No	p. 19; pp. 38-39
HF	Flame sensed while the gas valve isn't energized	Gas valve or control board; heater locks out	No; leave the heater off	p. 19; pp. 44-45
PF	Polarity failure: low voltage detected, insufficient ground path, or defective board	Supply voltage, ground and neutral connections	No	p. 19; pp. 42-43
BD	Bad board or secondary high-voltage fault	FC4 fuse, transformer, harness, fuse board	No	p. 19; pp. 34-35
EE	Bad board	Integrated control board	No	p. 19; pp. 36-37
CE	Communication error between the control board and the display	May clear with a power cycle; ribbon cable, display, board	One power cycle at the breaker	p. 19; pp. 36-37
SB	Keypad failure ("stuck button")	May clear with a power cycle; display/keypad assembly	One power cycle at the breaker	p. 19; pp. 38-39

Two displays that aren't faults:

• bo means the heater has been put in bypass mode so an external control can run it (H-Series guide, p. 13). With bo showing, the automation system or remote decides when the heater fires.
• LO with the pump off is normal (H-Series guide, p. 48).

LO — limit open

This is the H-Series code most likely to have a cause outside the heater. Hayward's chart starts by checking for adequate water flow and says that LO may be related to flow. Its first fix is to increase the flow rate or clean the filter (H-Series guide, pp. 46, 48).

What you can safely check: that the pump is running and on schedule, that the skimmer and pump baskets are empty, that the filter isn't loaded (a high reading on the filter gauge is a clue), and that the valves send water through the heater. Hayward lists minimum flows by model and a maximum of 125 gallons per minute, and warns that flow below the minimum can let the water boil and trip the high limits (H-Series guide, p. 61). On a variable-speed pump, a low-speed program may not reach the minimum.

When to stop: if LO stays on with good flow, Hayward's chart moves to the water pressure switch and its wiring, the high-limit switches, and (on indoor installs) the vent pressure switch and flue. On heaters made after February 2016, it also checks an exhaust gas limit switch (H-Series guide, pp. 46-51). Hayward describes that switch as a one-time safety: once it trips it has to be replaced, and the heat exchanger should be inspected for soot or damage (H-Series guide, p. 51). All of that is inside the heater.

IF — ignition failure

The heater tried to light and couldn't. In Hayward's sequence of operation, the heater retries three times, locks out showing IF, waits 60 minutes, tries three more times, and keeps retrying every 60 minutes as long as there is a call for heat (H-Series guide, p. 8).

Hayward's checks start with the main gas supply and then the heater's own gas valve. After that come the flame sensor and gas valve connections, gas pressures, the flame sensor itself, the blower air inlet plate, and the burner tubes and orifices (H-Series guide, pp. 52-55).

What you can safely check: whether other gas appliances in the house are working. If they aren't, the problem is the gas supply, not the heater. The heater's own gas valve and everything after it are inside the cabinet, so leave those to a technician.

HS and SF — water temperature

HS ("high sense") appears when the water sensor reads above 105°F, or when it sees a rise of more than 6°F within 60 seconds. Hayward says the inlet and outlet plumbed in reverse will often cause frequent HS codes. After that, its chart checks the thermistor and then the control board (H-Series guide, pp. 40-41). SF ("sensor failure") means the thermistor is reading out of range (H-Series guide, p. 41).

If HS started right after plumbing work at the pad, mention it when you call.

HF — flame with the gas valve off

HF means the heater sensed flame when the gas valve should have been closed. The control locks out and the blower runs continuously until the condition is corrected (H-Series guide, p. 45). Hayward's chart goes to the gas valve and the control board (H-Series guide, pp. 44-45). This is a combustion safety condition. Turn the heater off and have it checked rather than repeatedly resetting it.

AO, AC and IO — blower and ignitor

The H-Series runs a blower before ignition and checks a vacuum switch to confirm the blower is moving air (H-Series guide, p. 7). AO means that switch didn't close when it should have. AC means it was closed when it should have been open. IO means the ignitor circuit is open (H-Series guide, p. 19). Hayward's charts for all three involve resistance and voltage tests inside the heater (H-Series guide, pp. 38-39, 56-60).

PF, BD, EE — power and control board

PF ("polarity failure") appears when low voltage is detected, when the ground path isn't sufficient, or when the control board is defective. Hayward's chart checks that incoming power is within 10% of the required voltage and that the ground and neutral connections are clean and secure (H-Series guide, pp. 42-43). BD is a bad board or secondary high-voltage fault (H-Series guide, pp. 19, 34-35). EE means the integrated control board is defective (H-Series guide, p. 37). All three involve line voltage and belong to a technician.

CE and SB — display and keypad

CE is a communication error between the control board and the display. SB means the display board is acting as if a button is being held down. For both, Hayward's first step is to cycle the power, because the code may clear (H-Series guide, pp. 36-39). Switching the heater's breaker off and back on once is a reasonable thing to try. If the code comes back, leave it for a diagnosis.

HeatPro and Summit heat pump codes

Many of these codes appear in two forms, one used by the round HeatPro control and one by the square Summit-platform control. Hayward pairs them in its guide.

Code (either form)	What Hayward says it means	Usually points to (per Hayward's chart)	Safe to check yourself?	Guide page
PS / FLo	Water pressure switch open: low or no water flow	Pump off, time clock off, dirty filter, open bypass valve	Yes: pump, schedule, filter, valves	pp. 32-33
HI / HP	High-pressure switch open (above 590 psi; resets at 440 psi)	Restricted water flow, open bypass; minimum 30 gpm	Partly: flow checks only	pp. 25-26
LP	Low-pressure switch open (below 80 psi; resets at 120 psi)	Refrigerant leak; fan motor or capacitor; very cold air	Partly: outdoor temperature only	pp. 23-24
PO / OP	Water temperature sensor open	Sensor or wiring, then control board	No	pp. 27-28
Pc / SH	Water temperature sensor shorted	Sensor or wiring, then control board	No	pp. 27-28
dPO / cOP	Defrost (coil) temperature sensor open	Sensor or wiring, then control board	No	pp. 29-30
dPc / cSH	Defrost (coil) temperature sensor shorted	Sensor or wiring, then control board	No	pp. 29-30
FS / deF	Unit is in defrost	Normal in the low-to-mid 50s °F or colder	Yes: note the outdoor temperature	p. 35
Blank display	No low voltage reaching the control	Tripped breaker; on round units, a 1-amp fuse	Yes: the breaker, once	p. 34

PS / FLo — water flow

FLo appears on square units and PS on round units. Either way, the water pressure switch is open (heat pump guide, pp. 13, 33). Hayward says the switches occasionally fail, but most of these codes are flow-related. Open bypass valves, time clocks in the off cycle, pumps turned off and dirty filters account for the majority (heat pump guide, p. 33).

What you can safely check: the pump is on and within its schedule, the filter is clean, and any bypass around the heat pump is closed. On square units wired to a remote control, FLo also shows whenever the remote isn't calling for heat, which is normal (heat pump guide, p. 13).

HI / HP — high refrigerant pressure

The high-pressure switch opens above 590 psi and resets at 440 psi. Hayward says the most common cause is restricted water flow, and names an open bypass valve as a likely culprit. It notes that a heat pump needs at least 30 gallons per minute, and more at higher water temperatures. This often shows up when heating a spa to around 100°F (heat pump guide, pp. 25-26). The same flow checks as PS/FLo apply. If the code comes back after a few seconds of running, Hayward's chart points to the expansion valve, which is refrigerant-side diagnosis.

LP — low refrigerant pressure

The low-pressure switch opens below 80 psi and resets at 120 psi. Hayward says the most common cause is a loss of refrigerant from a leak. An intermittent LP can come from a bad fan motor or capacitor. Sustained outdoor temperatures below 21°F will also cause LP, and the switch closes on its own once the air rises above 40°F (heat pump guide, pp. 23-24). The only safe check for a homeowner is the weather. Anything involving gauges or the refrigerant circuit is a diagnosis for a technician.

Sensor codes — PO/OP, Pc/SH, dPO/cOP, dPc/cSH

These report an open or shorted temperature sensor, either the water sensor or the defrost (coil) sensor. Hayward's charts check the wiring and then compare the sensor's resistance to its chart, and replace the control board if the sensor checks good (heat pump guide, pp. 27-31). Nothing here can be checked from outside.

FS / deF — defrost

FS on square units and deF on round units mean the heat pump is defrosting: the compressor is off and the fan keeps running. Hayward calls this normal when the outdoor air is in the low-to-mid 50s or colder. Round units run up to three 15-minute fan cycles, and if the coil hasn't recovered they shut down for two hours showing deF. Square units stay in defrost until the coil sensor reaches 42°F. If FS or deF appears in warmer weather, Hayward points to a failing defrost sensor (heat pump guide, p. 35).

Blank display

Hayward says a blank display means no low voltage is reaching the control, and that a tripped breaker is a likely cause. On round units, a blown 1-amp fuse can also cause it (heat pump guide, p. 34). Check the breaker. If it trips again after one reset, leave it off.

Before you call: the start delay

Hayward heat pumps wait before starting, three minutes on square units and five on round units, and the delay restarts whenever power is interrupted. Hayward heat pumps also won't run when the pool pump is off (heat pump guide, p. 6). A heat pump that has just been switched on and isn't doing anything may simply be waiting.

Where to stop

Stop and leave the unit off if you smell gas (leave the area and call your gas utility first), if a breaker trips again after one reset, if a gas heater shows HF, or if the next step would mean removing a panel. Both Hayward guides are written for technicians working inside the unit, and the H-Series guide is clear that only qualified technicians should remove the panel (H-Series guide, p. 2).

Getting it diagnosed

A heater diagnostic reads the code against Hayward's documentation for your model, measures the flow through the heater, checks the pump speed and schedule behind that flow, and checks the filter and valve positions on the pad. On a heat pump, it also covers the fan, capacitor, sensors, board and switches, and the clearance around the air intake and discharge. You get a clear answer on what has failed and what fixing it involves.

A diagnostic is $120, and the $120 is credited toward your repair if you go ahead. Start from the pool heater diagnostic or heat pump page, or read the broader guide to a pool heater not heating.

Sources

• Hayward Industries, Universal H Series Heaters Troubleshooting Guide (HxxxFD(N/P)ASME), TSG-UHS16b (2017). Diagnostic code list: p. 19.
• Hayward Industries, Hayward/Summit Heat Pump Troubleshooting Guide, TSG-HTPMPa (2018). Error codes: pp. 23-35.
• Pentair, MasterTemp Pool and Spa Heater Installation and User's Guide, P/N 472592 Rev. Q (7/30/23), p. 42. Cited only for the gas-smell instructions.

Hayward, Universal H-Series, HeatPro and Summit are trademarks of Hayward Industries. Pentair and MasterTemp are trademarks of Pentair. They are named here only to identify equipment.