The most likely fix on a Hayward heater code: pull the filter and verify flow before you buy a single part. The two codes we see most on South Florida pads — LO on a Universal H-Series gas heater and HPon a HeatPro heat pump — both point at flow first and at the heater second. A loaded cartridge chokes circulation, the pressure switch never closes, and a perfectly healthy heater reports a fault. Note that code labels and reset sequences vary across the Hayward lines (Universal H-Series H150–H400, HeatPro, and the older H-Series analog units) — verify against the service manual that shipped with your unit.
Hayward error-code quick reference
| Code | Family | What it means | Field fix | DIY or pro |
|---|---|---|---|---|
| LO | H-Series gas | Low water flow — the pressure switch is open | Clean the filter first, then check valves, then the pressure switch ($250–$500) | Filter is DIY; switch is pro |
| IF / IO | H-Series gas | Ignition failure or lockout — no flame proven | Igniter, flame sensor, or gas valve ($300–$900) | Pro — gas |
| HS | H-Series gas | High-limit trip — the heater is overheating | Restore flow, descale the exchanger, or replace the limit switch ($250–$600) | Pro |
| SF | H-Series gas | Sensor fault — bad water-temp or stack sensor | Sensor replacement ($250–$450) | Pro |
| LP / HP | HeatPro heat pump | Low or high refrigerant pressure | HP is frequently a dirty coil or a flow problem — clean the coil and verify flow. Refrigerant work is licensed work. | Coil is DIY; refrigerant is pro |
| — | HeatPro heat pump | Won't heat below about 50°F | Nothing. That is normal heat-pump behavior in a cold snap, not a fault. | No action |
Why LO is the code you will see most
Every Hayward gas heater has a pressure switch that refuses to let the unit fire without circulation, and LO is that switch reporting it never closed. Nine times out of ten the switch is telling the truth and the problem is upstream: a cartridge that has gone a season too long, a skimmer basket packed with leaves after a storm, or a valve somebody moved and never moved back. Pull the filter and run the system before you touch the heater. If it fires, you just repaired the heater for the price of a rinse — and if a company ever “repaired” your Hayward without touching the filter, get a second opinion.
IF and IO: no flame proven
These are the ignition faults. The heater called for heat, ran its light-off sequence, and never proved flame. Three components own almost all of it: the igniter, the flame sensor, and the gas valve. Confirm the gas valve is actually open first — propane tanks run out and somebody closes a valve during a service call more often than anyone admits. A cracked igniter is visible on inspection. A dirty flame sensor lights and then drops out seconds later, which is the symptom worth separating from a true no-light. This is gas work and it belongs with a licensed tech.
HS: the heater is cooking itself
A high-limit trip means water is not carrying heat away fast enough. That is either low flow again or a heat exchanger scaled up on the inside. South Florida fill water at 200–450 ppm calcium hardness lays scale on the inside of an exchanger the same way it lays it on your tile, and a scaled exchanger runs hot on the fire side while the water leaves cold. Chronic HS on a heater with good flow is usually a descale, not a switch.
HeatPro faults: LP, HP, and the 50°F rule
On the heat-pump side, HP is the common one and it is usually not refrigerant at all— it is a coil packed with grass clippings, pollen, or salt film, or the same flow problem the gas units report as LO. Clean the coil, verify flow, and re-run it. If it still faults, that is refrigerant work and it requires an EPA-certified tech. The one call that is not a fault: a HeatPro that stops heating when the air drops near 50°F is behaving exactly as designed. Heat pumps pull warmth out of the air, and there is less of it to pull. Every January we get calls on this and the honest answer is that the equipment is fine.
South Florida failure modes
- Salt air on coastal pads. HeatPro coils within a mile of the water corrode and load up with salt film years earlier than inland units. Rinsing the coil is genuine preventive maintenance here, not a nicety.
- Scale from hard fill water. The same aquifer hardness that scales your tile scales the inside of a gas exchanger. This is what turns an occasional HS into a chronic one.
- Storm debris. A single storm can pack a skimmer basket and a coil at the same time, which produces an LO on the gas unit and an HP on the heat pump from one cause.
- Wasp nests in the burner tray. Common on units that sit idle through the warm months and then get called on in December.
When it is time to replace rather than repair
A heater past roughly 10 years with a failed exchanger is usually a replacement — the exchanger is the single most expensive part in the unit, and on a heater that age the burner tray and controls are not far behind. Repeated HS faults on a unit with verified good flow point the same direction. A heater killed by chemistry rather than age is the one worth being angry about: unbalanced water eats exchangers from the inside, which is why balanced chemistry is the cheapest heater insurance there is.
When to call a pro
Filter, basket, and valve checks are yours. Coil cleaning on a HeatPro is yours. Everything past that on a gas unit — igniter, flame sensor, gas valve, pressure switch, high limit, gas-pressure testing — is licensed work, and refrigerant work on a heat pump requires EPA certification. In Florida, residential pool repair is regulated by the DBPR under the RP and CPC license categories.
Frequently asked questions
LO means low water flow on a Universal H-Series gas heater — the pressure switch that has to close before the heater will fire never closed. Nine times out of ten the switch is telling the truth and the problem is upstream: a cartridge filter that has gone a season too long, a skimmer basket packed with leaves after a storm, or a valve someone moved and never moved back. Clean the filter and run the system before touching the heater. If the switch itself is the fault, that repair runs $250 to $500.
Both are ignition faults — the heater called for heat, ran its light-off sequence, and never proved flame. Three components own nearly all of it: the igniter, the flame sensor, and the gas valve. Confirm the gas valve is actually open first, because propane runs out and valves get closed during service calls more often than anyone admits. A cracked igniter shows on inspection. A dirty flame sensor lights and then drops out a few seconds later, which is worth separating from a true no-light. Expect $300 to $900, and this is gas work for a licensed tech.
A high-limit trip means water is not carrying heat away fast enough, which is either low flow again or a heat exchanger scaled up on the inside. South Florida fill water runs 200 to 450 ppm calcium hardness, and it lays scale inside an exchanger the same way it lays it on your tile — the fire side runs hot while the water leaves cold. Chronic HS on a heater with verified good flow is usually a descale rather than a switch. Budget $250 to $600.
Usually not. HP is a high refrigerant pressure fault, but the common causes are a coil packed with grass clippings, pollen, or salt film, or the same flow restriction the gas units report as LO. Clean the coil, verify flow, and re-run it before assuming refrigerant. If it still faults after that, it is genuine refrigerant work and requires an EPA-certified technician — that is not a homeowner job and not a general handyman job either.
If the air temperature is near or below about 50°F, it is behaving exactly as designed. A heat pump moves warmth out of the air into your water, and on a cold South Florida morning there is not enough of it to move. We field these calls every January and the honest answer is that the equipment is fine. If you want reliable heat through a cold snap, that is a gas heater's job, not a heat pump's.
By fault: a pressure-switch repair behind an LO code runs $250 to $500; ignition faults behind IF or IO run $300 to $900 depending on whether it is the igniter, the flame sensor, or the gas valve; a high-limit trip runs $250 to $600 and may be a descale rather than a part; a sensor fault behind SF runs $250 to $450. Before any of that, clean the filter — a meaningful share of Hayward heater calls end there, at the cost of a rinse.
Hayward still throwing a code after the flow check?
Nine times out of ten an LO or an HP is flow, not the heater. If the filter is clean and the code is still there, we diagnose Hayward H-Series and HeatPro units across Palm Beach and Broward — flat-rate quote in writing before any part is ordered.