First cold morning of the season, and the display says IF. Every code below comes from Hayward's Universal H-Series Diagnostics Manual, and one piece of internet advice about the SB code is flatly wrong.
Redzone Pools repairs Hayward heaters across Cypress, Tomball, Katy, Spring and Greater Houston — licensed, insured, usually same day.
When the service light comes on, the display shows a two-letter code. There are thirteen: AC, AO, BD, CE, EE, HF, HS, IF, IO, LO, PF, SB and SF. Note it before you cycle power; several clear themselves.
The manual covers the Universal H-Series HxxxFD, H150 through H400; older non-FD H-Series units and millivolt heaters aren't covered. Covered model numbers read like H250FDN (N, natural gas) or H400FDP (P, propane). If yours doesn't include FD, tell us the model and what, if anything, the display shows.
Codes and steps are from Hayward's 2014 manual; the who-does-it calls are ours. The right-hand column is a map, not a DIY procedure.
| Code | What it means | What to do / how it clears |
|---|---|---|
| AC | Blower vacuum switch closed when it should be open. | Switch continuity; blower running with heater off means the board. |
| AO | Blower vacuum switch open. | Wiring, tubing, voltage plug, blower resistance; then switch or board. |
| BD | Bad board or secondary high-voltage fault. | FC4 fuse, then voltage checks: board, harness, fuse board or transformer. |
| CE | Control board to display communication error. | May clear on a power cycle; then ribbon cable, display or keypad, board. |
| EE | Bad board. | Replace the control board (ICB). |
| HF | Flame present with the gas valve not energized. | Stop and call. Lockout, blower running until corrected, then auto-restart 2 minutes later; Hayward's reset step, a line-power cycle, is a technician's job. Gas valve or board. |
| HS | Water over 105°F, and/or a 6° rise in 60 seconds. | Lockout; auto-restarts 2 minutes below 105°F. May pair with SF; sensor, reversed water connections, board. |
| IF | Ignition failure: retried three times without flame, then locked out. | Retries hourly while calling for heat. Gas shutoff, pressures, wiring, inlet plate, spider webs, moisture. |
| IO | Igniter circuit open. | Igniter wiring and plug; igniter should read 8–25 ohms (between 20 and 140°F). |
| LO | Limit open: water pressure, vent pressure or temperature limit switch. Normal when the pump is off. | Pump on, flow above minimum, clean filter; then pressure switch, limit switches, vent switch (indoor only). |
| PF | Polarity reversed, low voltage, poor ground, or defective board. | Resets immediately once the fault is corrected. |
| SB | Stuck button: held closed over 30 seconds. Not standby. | Keypad ohm test (page 22); keypad or display board. |
| SF | Temperature sensor (thermistor) input failure. | Both legs should read the same, 10k ohms at 77°F; sensor, otherwise board. |
Three reset themselves (HS two minutes after the water cools below 105°F, HF two minutes after the fault clears, PF the instant the fault is corrected); IF retries hourly while there's a call for heat. LO, IF and CE are the only ones with a step you can take yourself; HF's first step is also a power cycle, but flame with the gas valve off is a call, not a retry. The rest need a meter before anyone names a part.
On a Hayward pool heater the IF code is ignition failure. The control confirms the blower vacuum switch is open, runs a 20-second pre-purge while the igniter heats, and confirms the switch has closed. Then, at proper igniter temperature, a four-second trial: gas valve open, blower off for one second, control watching for flame. None, and the valve closes, the blower post-purges for 30 seconds, and it starts again.
The control retries three times (Hayward's words: "retries 3 times until lockout"), then locks out and posts IF. It waits 60 minutes, retries three more, and repeats hourly while there's a call for heat.
What IF does not tell you is why. The burner may never have lit, or it lit and a fouled, unplugged or wrong-length flame sensor never saw it. From the deck those are identical, so swapping the igniter can change nothing. Hayward's flowchart never ends at replace the igniter; an open igniter circuit is IO, and the last box is replace the flame sensor.
Hayward's IF checklist, in order. Only the outside shutoff in item 1 is yours; the valve inside the cabinet is ours.
1. Main gas shutoff outside the heater open, and the gas valve inside the heater ON. Shut off last season? Start there.
2. Flame sensor and gas valve wiring secure.
3. Gas static, load and manifold pressures correct; never adjust the valve if incoming pressure is wrong.
4. Units built before 4/14/2009: a 3-inch flame sensor replaced with the 5-inch.
5. 22–28 VAC at the gas valve during the trial. Present, valve doesn't open: gas valve. Absent: board.
6. Blower air inlet plate correct, undamaged, unblocked.
7. Orifices and burners inspected for blockage (Hayward's word is spider webs), and the combustion chamber checked for moisture from roof run-off or sprinklers.
Item 7 is Houston: burners open to whatever moved in over an idle Gulf Coast summer, a sprinkler keeping the chamber damp. The full idle-season pattern is in why Houston heaters won't fire on the first cold morning. Items 2 onward mean the cabinet open, and Hayward says only qualified technicians should attempt repairs. Redzone is TICL #1465 licensed and insured for it.
LO is Limit Open: the water pressure switch, the temperature limit switches or (indoors only) the vent pressure switch isn't closed. Hayward is plain: the LO code is normal when the pump is turned off. Heater calling before the pump's schedule starts? LO. Not a fault.
Pump running, Hayward checks flow before the switch: above the model's minimum, or backwash or clean the filter. Only then the pressure switch, high limit switches and, indoors, the vent switch.
Minimums: H150FD and H200FD 20 GPM, H250FD and H300FD 25 GPM, H350FD and H400FD 30 GPM, maximum 125. Below that, Hayward warns of dry firing and boiling.
If cleaning doesn't restore flow, look at the filter and circulation side before the heater, though Hayward notes the heater's own internal bypass can also cause low flow. A variable-speed pump idling on a low speed can move less than the minimum, holding the water pressure switch open and producing LO with the pump visibly running. Raise the speed above the heater's minimum before condemning the switch.
People search "Hayward HS code high limit," but here the temperature limit switches report through LO, not HS. HS is High Temperature Sense: above 105°F the heater locks out and restarts automatically 2 minutes after the water drops below 105°F. It also trips on a rise of 6° in 60 seconds.
HS can pair with SF, the temperature sensor fault, and a new sensor can cure it; check the water connections aren't reversed; otherwise, the board.
HF deserves real respect: flame sensed with the gas valve off. The heater locks out and runs the blower until corrected; no 24 VAC at the valve with manifold pressure present means the gas valve has failed.
Fires but never warms the water? See a pool heater that runs but won't heat.
The SB code gets read as "standby" because the letters fit. Hayward's manual says otherwise. SB means Stuck Button: the display board is receiving a continuous closed circuit on one of the buttons for more than 30 seconds. The code table lists it as keypad failure.
Standby is a mode you choose with the Mode button; no code exists to report it. An SB isn't a heater resting; it's a keypad the control thinks is being pressed.
Hayward's SB page sends you to the keypad ohm test on page 22 (the same page checks the display board isn't wet or fouled with debris): open unpressed, under 100 ohms pressed. Wrong readings: keypad. Correct: display board.
Don't hold a button down for half a minute; that's precisely what SB reports. The manual notes a keypad entry may take 5 to 10 seconds to register in certain situations. Slow is not stuck.
Reasonable to try yourself: note the code; confirm the pump is running and the filter is clean; set temperature above water temperature, Pool or Spa mode, not Standby; main gas shutoff open; see whether sprinklers or roof run-off reach the cabinet; and for a CE, one power cycle.
Stop and call: IF that keeps returning; anything involving gas pressure, the gas valve, orifices or the burner tray; HF, every time; HS that repeats; any code that needs a meter or the cabinet open; and any smell of gas.
Pentair owner? See the MasterTemp error code guide. Otherwise, pool heater repair is our day job.
Ignition failure: Hayward's control retried the four-second trial three times without seeing flame, then locked out. The code doesn't say whether the burner never lit or lit unseen by the flame sensor; that takes a meter, not a guessed part.
Yes. Three retries to lockout, a 60-minute wait, three more, then hourly while there's a call for heat. So one that lit on a retry isn't necessarily fixed.
LO means a limit switch is open; it's normal with the pump off. Pump running, Hayward checks flow before the switch (20 GPM minimum for the H150FD and H200FD, 25 for the H250FD and H300FD, 30 for the H350FD and H400FD) and cleans the filter first.
Not exactly. HS is High Temperature Sense: lockout above 105 degrees F, automatic restart 2 minutes after the water drops below 105 degrees F, and a trip on a rise of 6 degrees in 60 seconds. The temperature limit switches are a separate safety that reports as LO.
No. In Hayward's manual SB is Stuck Button (a keypad button held closed for more than 30 seconds), listed as keypad failure. Standby is a mode you select with the Mode button, not a diagnostic code. Hayward's step is the keypad ohm test on page 22, after checking the display board is dry and free of debris: wrong readings mean the keypad, correct readings the display board.
Set temperature above water temperature, Pool or Spa mode rather than Standby, pump running with a clean filter (pump off means LO), main gas shutoff open. Tries to light and drops out repeatedly, then quits? That's IF, and past the gas shutoff it's a licensed technician's job.
Tell us the code, the model and whether the pump is running; we can usually say on the phone whether it's a filter clean, a keypad, or a cabinet-open job. TICL #1465 licensed, insured, serving Cypress and Greater Houston.