Common symptoms
- The heater screen is on, but nothing happens when you raise the set point.
- The screen shows a code such as LO, IF, ERR PS, CHECK FLOW or Water Sw Open.
- A gas heater’s blower runs, you hear it try to light, and then it stops.
- The burner lights, runs a short while, then shuts off with a high limit code.
- A heat pump’s fan spins, but the pool stays cold for days.
- The pool warms up, then stops short of your set temperature.
Quick checks before anything else
- The heater is on, in Pool or Spa mode, and set above the current water temperature.
- The filter pump is running and its timer is in an on cycle.
- The filter is clean and the skimmer and pump baskets are empty.
- Every valve between the pump and heater is open, and any bypass around the heater is closed.
- The gas valve is on and the propane tank has fuel.
- The breaker for the heater is on.
- For a heat pump, leaves and debris are cleared from the coil on the sides and top.
What causes a pool heater to stop working?
- Low water flow The heater shows a flow or pressure switch code and will not start.
- No gas, or air in the gas line The igniter works but the burner never lights, often after a propane refill.
- Ignition lockout After 3 failed tries to light, the heater stops trying and shows an ignition code.
- High limit trip The burner lights, then shuts off because water inside the heater got too hot, most often from low flow.
- Settings and lockouts A set point below the water temperature, or a maximum temperature lock, stops heating with no error at all.
- Heat pump conditions A start delay, cold air, or defrost mode makes a working heat pump look broken.
- Call for heatWater is 1 degree below the set point
- Pre-purgeBlower runs about 20 seconds while the igniter heats up
- Trial for ignitionGas valve opens for a 4-second trial
- Flame sensed?
Yes: the burner runs until the water reaches the set point, then the blower runs a 30-second post purge.
No: it tries 3 times, then locks out with an IF code. It waits 60 minutes and tries 3 more times, and keeps retrying every 60 minutes while there is a call for heat.
Step-by-step: fix a pool heater that won’t heat
When your pool heater is not working, we start with the free checks and leave gas and wiring for last. Often the heater is fine and something upstream is starving it of water. Our pool heater problems page explains how each part works.
- Read the display first. Write down any code before you change anything, since a reset can clear it. Codes differ by brand and model, so match yours in our error code lookup. Flow codes point to steps 3 to 5, ignition codes to steps 6 and 8.
- Check the mode and set point. The heater must be in Pool or Spa mode, not off or standby. Pentair says the set point must be above the actual water temperature or the burner will not fire. Hayward’s Universal H-Series starts when the water is 1 degree below the set point, so a set point near the current temperature can look like a dead heater.
- Make sure the pump is running. A heater only heats while the filter pump pushes water through it, and Hayward says its heat pumps will not run at all with the pump off. Check the timer too: Jandy’s fixes for a “Check Flow” message include setting the time clock to the current time. On a two-speed or variable speed pump, run a higher speed. Hayward says some two-speed pumps must be on high to close the heater’s flow switch.
- Clean the filter and baskets. Pentair says its ERR PS message usually means the filter or skimmers need cleaning, and some filters need backwashing (running water backward to flush dirt out). If your filter gauge reads well above its clean pressure, see our pool filter pressure guide.
- Open valves and close bypasses. Hayward says open bypass valves, timers in their off cycle, pumps turned off and dirty filters cause the majority of its flow errors. Jandy also says to turn off fountains and waterfalls that pull water away before the heater. Hayward’s heat pump chart adds: unhook cleaning devices. If the pump will not hold water, fix that first with our pool pump not priming guide.
- Check the gas supply. Make sure the propane tank has fuel and the gas valve is on. Pentair says to turn its gas control only by hand, never with tools. After a propane refill or a long shutdown, air in the line can stop the burner. Jandy’s fix is to cycle the ignition until the air is out. Pentair says to press OFF, wait five minutes, then turn the heater back on, and repeat until it fires.
- Check the power. Gas heaters need electricity for the control board and blower, and heat pumps run on 240 volts. Hayward says a tripped breaker is the likely cause of a blank heat pump display. If a breaker trips again after you reset it, stop and call an electrician.
- Clear an ignition lockout once. After 3 failed tries, gas heaters stop. Hayward’s Universal H retries on its own every 60 minutes. Pentair’s ERR IGN needs the HEATER OFF button. Jandy’s ignition board flashes its LED 3 times for a soft lockout. Raypak says to interrupt power to the heater. If it locks out again with good gas and flow, call a technician.
- Look for high limit trips. A high limit is a heat switch that shuts the burner off when water inside the heater gets too hot. On a Pentair MasterTemp, ERR HLS appears above 135 F and clears by itself once the water cools below that. Low flow is the usual reason, so go back to steps 3 to 5. Raypak adds a less obvious cause: the pump should keep running at least 5 minutes after a heating cycle ends, or leftover heat can trip the limit.
- Give a heat pump time. Heat pumps wait before the compressor starts: 5 minutes on Hayward HeatPro and Pentair UltraTemp units. Once it runs, feel the air leaving the top. Hayward says it should be 15 to 20 F cooler than the outside air, which is the best sign the unit is heating. Jandy says a new install or a pool that has cooled a lot may need 24 to 48 hours of nonstop running.
- Check maximum temperature locks. If the pool stops short of the set point with no code, look for a cap. Hayward’s Universal H-Series has a temperature lockout with defaults of 90 F for pool and 104 F for spa. Pentair has POOL MAX and SPA MAX settings from 65 to 104 F.
Stop. If you smell gas, do not try to light the heater, do not touch electrical switches, and call your gas supplier from a neighbor’s phone, as Pentair’s manual says. Never jump or bypass a pressure switch, flow switch or high limit. Pentair also says not to use a heater if any part has been under water; have a technician inspect it first.
Hayward vs Pentair vs Jandy vs Raypak: codes and resets
All four gas heaters stop for the same reasons. What changes is the wording and how you clear it.
| Gas heater | Flow message | Ignition message | How it clears |
|---|---|---|---|
| Hayward Universal H | LO (water pressure, vent pressure or limit switch fault) | IF | Retries every 60 minutes after a lockout |
| Pentair MasterTemp | ERR PS | ERR IGN | PS and HLS clear by themselves; IGN needs HEATER OFF |
| Jandy JXi | CHECK FLOW | LED flashes 3 times | Soft lockout after 3 tries |
| Raypak digital | Water Sw Open | Ignition Lockout | Interrupt power; some ASME high limits need the MODE button |
Minimum flow differs by size: 20 to 40 gallons per minute (GPM) for Hayward Universal H, Pentair MasterTemp and Raypak 206A to 406A heaters, and 30 GPM for the Jandy JXi. Your model’s number is in its manual.
Heat pumps work differently. They use refrigerant and outside air, so they also stop for weather. Hayward heat pumps may show dEF or FS in defrost when the air is in the low to mid 50s, which is normal, and an LP code if the air stays below 21 F. A flow error on Hayward’s inverter heat pumps reads E03; see our pool heat pump error E3 guide.
When to call a pool or spa pro
- You smell gas, see soot or scorch marks, or the heater has been under water.
- A flow code stays on with a clean filter, a running pump and open valves. The pressure switch may need adjusting or replacing.
- Pentair shows ERR HLS, ERR AFS, ERR IGN, ERR AGS or ERR SFS. Pentair says to shut the heater down and have a qualified technician check it.
- A heat pump shows LP or HP codes in warm weather. Refrigerant work falls under EPA rules, as Hayward’s guide notes.
- The breaker trips again after a reset.
Common questions
What causes a pool heater to stop working?
Low water flow is the most common cause in the makers’ guides. After flow, look at the gas supply, an ignition lockout, a tripped breaker and the set point.
How do you reset a pool heater?
Fix the cause, then reset the way your brand says. Pentair flow and high limit errors clear on their own, while ignition errors need the HEATER OFF button. Raypak says to interrupt power. Resetting over and over without fixing flow or gas only brings the code back.
Is there a reset button on a Hayward pool heater?
Hayward’s Universal H-Series troubleshooting guide does not describe a reset button. After an IF ignition lockout, the control retries by itself every 60 minutes for as long as there is a call for heat. For its other diagnostic codes, the guide sends you to a Hayward authorized service center.
Why is my pool heater running but the water isn’t getting hot?
On a heat pump, check the air at the top first: if it is 15 to 20 F cooler than the air going in, Hayward says the unit is heating and needs more run time. On a gas heater, Jandy lists a filter pump that does not run long enough, a thermal regulating valve stuck open, and plumbing hooked up backward.
What is the average lifespan of a pool heater?
Hayward, Pentair, Jandy and Raypak do not publish a lifespan in the manuals we checked. Hayward’s guide shows what damages a heat exchanger: low flow, low pH, high sanitizer levels, high pH, alkalinity or calcium, and freezing. Keeping your pool chemistry in range and the flow up is what the makers point to.
How expensive is it to fix a pool heater?
Many fixes on this list cost nothing: cleaning the filter, opening a valve, raising the pump speed or refilling propane. Igniters, switches and boards vary in price by model, and pros bill by the visit or hour, so give them the model, serial number and code.
