Your pool heater will not fire, shows an error code, or runs all day while the water stays cold. Most pool heater problems come down to three things: not enough water flow, no gas or power, or a safety switch doing its job. This page explains how gas heaters and heat pumps work, which parts fail, what the common codes mean, the numbers from the makers’ manuals, and where DIY should stop.
How does a pool heater work?
A gas heater burns natural gas or propane under a heat exchanger, a bundle of tubes that pool water flows through. A heat pump burns nothing. It uses electricity and refrigerant to pull heat from the outside air into the water, like an air conditioner in reverse.
- The pump runs. The filter pump pushes water through the heater. Hayward says its heat pumps will not operate when the pool pump is off, and gas heaters need flow too.
- Flow is proven. A water pressure switch or flow switch closes when enough water is moving. If it stays open, the heater shows a flow code and waits.
- The thermostat calls for heat. A Hayward Universal H-Series heater starts when the water is 1 degree below the set point.
- Gas heater: purge, then light. A blower clears the burner box while the igniter heats up, then the gas valve opens. A flame sensor must see the flame, or the heater tries again and then locks out.
- Heat pump: delay, then compressor. The compressor waits out a protection timer, 5 minutes on Hayward HeatPro and Pentair UltraTemp units.
- Limits stand guard. High limit switches shut a gas heater off if the water inside gets too hot. Heat pumps use refrigerant pressure switches.
Which pool heater parts fail, and what are the signs?
| Part | What it does | Sign it is failing |
|---|---|---|
| Water pressure or flow switch | Proves water is moving | Flow code even with the pump running and a clean filter |
| Igniter and flame sensor | Light the burner and confirm the flame | Blower runs, no flame, then an ignition lockout code |
| Gas valve and supply | Feed gas to the burner | Igniter lights but the burner does not; Jandy lists air in the gas line and low gas pressure |
| High limit switch | Cuts heat if water in the heater gets too hot | Burner lights, then quits with a high limit code, often from low flow |
| Heat exchanger | Moves heat into the water | Leaks or soot; Hayward links damage to low pH, high sanitizer, high calcium and freezing |
| Heat pump fan and coil | Pull heat from the air | Air leaving the top is no cooler than the air going in |
| Refrigerant pressure switches | Stop the compressor at unsafe pressures | HP or HI code (often restricted water flow) or LP code (often a refrigerant leak) |
What should I check first when my pool heater is not heating?
- Mode and set point. The heater should be on, in pool or spa mode, and set above the water temperature. Jandy tells its own techs to confirm this first.
- Pump and timer. Hayward says pumps turned off, timers in their off cycle, dirty filters and open bypass valves cause most of its flow codes. On a variable speed pump, run a speed that meets the heater’s minimum flow.
- Filter and baskets. Clean the filter and empty the baskets. Pentair says its ERR PS message usually means exactly this. See our pool filter problems page.
- Valves. Open every valve between the pump and the heater, and close any bypass around it.
- Gas. Check the propane tank and gas valve. After a refill, Jandy says to cycle the ignition until the air is out of the line.
- Breaker. Gas heaters need power for the control and blower. Heat pumps run on 240 volts.
- Heat pump coil. Clear leaves from the sides and top.
Safety first. If you smell gas, do not try to light the heater. Turn off the gas, move away, and call your gas company from somewhere else. Never jump or bypass a pressure switch, flow switch or high limit; Pentair warns this risks fire or explosion. Shut off the breaker before opening any panel. For a gas heater installed indoors, Jandy strongly recommends carbon monoxide detectors near it and in occupied rooms next to it.
Pool heater numbers to know
These numbers come from the makers’ own manuals and troubleshooting guides. Check the label and manual on your unit, since sizes differ.
| Spec | Gas heaters | Heat pumps |
|---|---|---|
| Minimum water flow | Hayward Universal H, Pentair MasterTemp, Raypak Digital: 20 to 40 GPM by size. Jandy JXi: 30 GPM | Hayward: 30 GPM, up to 40 GPM for spa heating. Pentair UltraTemp: 30 GPM. AquaCal: see your model’s manual |
| Maximum water flow | Hayward: 125 GPM. Pentair: 120 GPM. Jandy and Raypak: 100 GPM | Pentair UltraTemp: 120 GPM. Others: see your model’s manual |
| Tries before lockout | Hayward: 3, then retries every 60 minutes. Jandy: 3, then a soft lockout | Not used |
| Start delay | Pentair: gas valve opens about 20 seconds after the call for heat | Hayward HeatPro and Pentair UltraTemp: 5 minutes |
| High limits | Pentair MasterTemp: high limit opens above 135 F, gas shutoff above 140 F | Pentair UltraTemp: high water temp alarm above 107 F |
| Highest set point | Hayward and Pentair: 104 F. Raypak: 104 F by default | See your model’s manual |
| Air temperature drop when heating | Not used | Hayward: 15 to 20 F. AquaCal: 9 to 12 F |
| Cold weather | Raypak: locks out with water below 36 F | Hayward: LP code if air stays below 21 F |
Hayward vs Pentair vs Jandy vs Raypak: what changes when you troubleshoot?
All four brands stop for the same reasons: low flow, no flame, or too much heat. What changes is the wording on the screen.
| Brand | Code | What the maker says it means |
|---|---|---|
| Hayward Universal H | IF / LO / HS | Ignition failure / pressure or limit switch fault / return water too hot or heating too fast |
| Pentair MasterTemp | ERR PS / ERR HLS / ERR IGN | Not enough water flow / high limit open / could not light the heater |
| Jandy JXi | CHECK FLOW / LED 3 flashes | Flow or pressure switch problem / ignition lockout |
| Raypak Digital | Water Sw Open / Ignition Lockout | Water pressure switch open / burner did not light |
| Hayward HeatPro | FLO or PS / HP or HI / LP / dEF | No water flow / high refrigerant pressure / low refrigerant pressure / normal defrost |
| Pentair UltraTemp, AquaCal | LOW WATER FLOW / FLO | No water flow detected |
Parts do not swap between brands, so note the model and serial number before you order.
When should you call a pool or spa pro?
- Gas valve or gas pressure. Testing takes a manometer, a gauge that reads gas pressure.
- Refrigerant. Heat pump leaks and recharging fall under EPA refrigerant rules, as Hayward’s guide notes.
- Codes that come back. If a code returns after you have confirmed good flow, the switch, igniter or board needs testing with a meter.
- Soot, scorch marks, or a leaking heat exchanger. Shut the heater down until it is checked.
Pool pros bill by the visit or by the hour, so do the cheap checks first.
Common questions
How do I reset my pool heater?
Fix the cause, then turn the heater off and back on at its control. Pentair says flow and high limit errors clear by themselves once fixed, while ignition, gas shutoff and flue errors need the HEATER OFF button or a power cycle. Hayward’s Universal H-Series retries on its own every 60 minutes after an ignition lockout.
What does the E3 or E03 error code mean on a pool heat pump?
On Hayward’s inverter heat pumps, E03 means the flow switch sees no water, or too little water, moving through the unit. Hayward’s fix is to check the water flow and the pump. Codes are not standard across brands, so check your own manual.
Why is my pool heater running but not heating?
For a heat pump, feel the air. Hayward says air leaving the top should be 15 to 20 F cooler than the air going in; if it is, the unit works and needs more run time. For a gas heater, Jandy lists a stuck-open internal bypass valve and backwards plumbing as causes of low heat.
Why isn’t my pool heater reaching the set temperature?
Usually run time. A heater only heats while the pump runs, so a short pump schedule caps how warm the pool gets. Heat pumps also slow down as the air cools, and Hayward units may go into defrost when the air is in the low to mid 50s.
Why is my pool heater not kicking on?
If nothing happens, check the breaker, the mode and the set point. If the screen shows a flow code, check the pump, filter and valves. Heat pumps also wait 3 to 5 minutes after power comes back, which Hayward says protects the compressor.
How expensive is it to fix a pool heater?
Many fixes cost nothing: cleaning the filter, opening a valve, raising the pump speed or refilling propane. Switches, igniters and boards vary by brand and model, and pros bill by the visit or hour, so have the model number ready for a quote.
What is the average lifespan of a pool heater?
Hayward, Pentair, Jandy and Raypak do not publish a lifespan. Their manuals point to what shortens one: low flow, poor water chemistry and freezing. Raypak says free chlorine must not exceed 5 ppm (parts per million), so keep your pool chemistry in range.