Common symptoms
- The heat pump display shows E03 and the compressor and fan stay off.
- E03 shows up whenever the pool pump’s timer turns the pump off.
- The code appears a few minutes after start-up, or after you cleaned or backwashed the filter.
- The heat pump runs on high pump speed but shows E03 on low speed.
- Water barely moves out of the pool return jets.
- The code returns every few days as the filter gets dirtier.
Quick checks before anything else
- The pool pump is on, and its timer is in an on cycle.
- Water is pushing out of the pool return jets.
- The skimmer basket and the pump basket are empty.
- The filter pressure is not far above its normal clean reading.
- The pool water is high enough that the skimmer is not pulling air.
- Any bypass valve around the heat pump is closed, and the valves to it are open.
What does E3 or E03 mean on a pool heat pump?
On Hayward heat pumps, E03 is a flow error. Hayward’s manuals list it as “Flow Switch Prot.” with the reason “No/Little water in water system.” The flow switch is a small switch in the heat pump’s water line that closes only when enough water is moving. When it stays open, the control keeps the compressor off so the unit cannot damage itself. Some people write it as E3; Hayward’s manuals print it as E03.
Codes are not standard across brands. The E03 meaning on this page comes from Hayward’s documents. On another brand, E3 may mean something else, so check the code table in your own manual or in our error code lookup before you start.
What causes a flow error?
- Pump off or on a timer The heat pump is meant to stop when the pump stops, so E03 appears during every off cycle.
- Dirty filter or full baskets Flow drops as the filter clogs, so the code shows up after days of normal running.
- Open bypass or closed valve Water goes around the heat pump instead of through it.
- Pump speed too low A variable speed or two-speed pump on low may not move enough water to close the switch.
- Water features stealing flow Fountains, waterfalls or a suction cleaner pull water away from the heat pump.
- Bad or misplaced flow switch The code stays on with strong flow. This one needs a technician.
- Pump on, water movingCheck the pump runs and water reaches the pool return
- Flow switch orientationTechnician confirms the switch is mounted the right way
- Skimmer, basket, filterClean them and recheck
- BypassSlowly close an open bypass and watch the code
- Did E03 clear?
Yes: note the filter pressure and pump speed that worked, and keep the bypass where it is.
No: a technician tests the flow switch for continuity with the pump running. No continuity means a new switch; continuity means the control board is the problem.
Step-by-step: clear a heat pump E03 flow error
When your pool heat pump shows error E3 or E03, we follow Hayward’s own order, which starts with the pump and ends with parts. Do each step, then give the heat pump a few minutes, because it waits out a start delay before the compressor runs. For how heat pumps and gas heaters work, see our pool heater problems page.
- Confirm the pump is running. Hayward says to verify the pump is not only on but actually circulating water through the heat pump. Check the timer or automation schedule. If the code only shows while the pump is off, that is normal: Hayward’s start-up check has you turn the filter pump off and confirm the heat pump stops on its own.
- Check the pool return. Put your hand in front of a return jet. You should feel a steady push of water. Weak or no flow means the problem is before the heat pump, at the pump or filter.
- Empty the baskets. Clean the skimmer basket and the pump basket (the strainer under the clear lid on the pump). If the pump has lost its prime, meaning it is running without water inside, our pool pump not priming guide covers that first.
- Clean or backwash the filter. Look at the filter pressure gauge. A reading well above its clean pressure means a clogged filter, which cuts flow. Clean a cartridge, or backwash a sand or DE filter as its manual says. Our pool filter pressure guide explains the readings. Hayward says that if the code clears after cleaning, write down the filter pressure and pump speed so you know where trouble starts next time.
- Check the water level. Jandy’s heat pump manual says to check the pool water level when its no-flow fault shows. If the water drops near the bottom of the skimmer opening, the skimmer pulls air instead of water. Top up the pool and recheck.
- Close the bypass and open the valves. Many installs have a bypass valve that sends water around the heat pump. Hayward’s fix is to close it slowly while you watch the display. If E03 clears, close it fully or leave it where the code went away. Make sure every other valve to the heat pump is open.
- Turn off water features. Jandy says to temporarily turn off fountains and waterfalls that take water before it reaches the heat pump. Hayward’s troubleshooting chart also says to unhook cleaning devices. If the code clears, run the features and the heat pump at different times, or raise the pump speed.
- Raise the pump speed. On a variable speed or two-speed pump, try a higher speed. Hayward says some two-speed pumps only meet the flow switch’s minimum on high speed. If the plumbing cannot deliver the minimum flow at all, Hayward says not to run the heater until the installation is corrected.
- Know when to stop. If E03 stays on with a clean filter, a running pump, open valves and a closed bypass, the flow switch itself is next. Hayward’s technician steps check the switch’s mounting direction, then test it for continuity with a meter. A failed switch gets replaced; a good switch points to the control board. Both jobs mean opening a panel with 240 volts inside.
Stop. Never jump, bypass or tape over a flow switch or pressure switch. It is there so the heat pump cannot run without water. Pool heat pumps run on 240 volts, so turn off the breaker before anyone opens a panel.
E03 and related Hayward heat pump codes
Hayward’s newer heat pumps, including the HP50HA, HP50HA2 and HP50CLEE to HP75CLEE models, use a numbered code list. Several codes besides E03 point back to water flow.
| Code | What Hayward says it means | Next step |
|---|---|---|
| E03 | Flow switch protection: no or little water in the system | Check water flow and the pump |
| E06 | Inlet and outlet temperatures too far apart (more than 58 F on the HP50HA, where about 3.5 F is expected) | Check flow and the bypass |
| E07 | Antifreeze protection: water flow not enough | Check flow and for a jammed system |
| E05, E19, E29 | Water or air temperature too low | Check whether the water or air is too cold |
| E01, E02 | High or low refrigerant pressure | Call a technician |
Hayward vs Pentair vs Jandy: the same problem, different words
Not every heat pump uses E03 for low flow. The fix is the same, but the message changes.
- Older Hayward HeatPro and Summit units show PS or FLO. Hayward says most of these errors come from open bypass valves, timers in their off cycle, pumps turned off and dirty filters. These units need at least 30 gallons per minute (GPM), and Hayward says at least 40 GPM may be needed when heating a spa.
- Pentair UltraTemp shows a LOW WATER FLOW alarm with a red SERVICE light. Pentair adds a dirty pump impeller and suction air leaks to the usual list, and needs 30 GPM minimum. If the return pipe to the pool is very short, Pentair says back pressure may be too low to close the switch, and a directional fitting on the return can fix it.
- Jandy VersaTemp JRT shows FAULT NO FLOW. Its minimum is 20 or 30 GPM depending on the model.
Smaller Hayward units need less flow. The HP50HA2, for example, lists 16 GPM minimum and 25 GPM maximum. Your model’s numbers are on its spec sheet.
When to call a pool or spa pro
- E03 stays on with a running pump, a clean filter, open valves and a closed bypass.
- The heat pump keeps running after you turn the pool pump off. The flow switch is not doing its job.
- The pressure switch needs adjusting. Pentair says to adjust it only when the unit will not run with proper flow or will not shut off with the pump off.
- Codes E01 or E02 show up. Refrigerant work falls under EPA rules.
- Your heat pump sits more than 6 feet below the pool surface; Pentair says an external flow switch is needed there.
If the heat pump runs with no code and still will not warm the pool, our pool heater not working guide covers that.
Common questions
What does the E3 error code mean on my pool heat pump?
On Hayward heat pumps, E03 means the flow switch sees no water or too little water moving through the unit. The heat pump will not run until flow returns. Other brands may use E3 for something else, so confirm it in your manual.
How do I fix the E03 error code?
Restore water flow. Make sure the pump is running and water reaches the pool returns, empty the baskets, clean the filter, and slowly close any bypass around the heat pump. If the code stays with good flow, have a technician test the flow switch.
What does the error code E03 mean on a Hayward heat pump?
Hayward calls it “Flow Switch Prot.” and says the cause is no or little water in the system. Its fix is to check the water flow and the pump. On older HeatPro and Summit models, the same problem shows as PS or FLO instead.
How do I reset an error code on a heat pump?
Fix the cause first, because a flow switch closes again on its own once water moves. Then expect a wait: Hayward heat pumps have a built-in restart delay of about 3 to 5 minutes, depending on the model, before the compressor starts. Turning the power off and on only restarts that delay.
Why does my heat pump show E03 when the pump is running?
The pump may run without moving enough water. A clogged filter, full baskets, a low speed setting, an open bypass, or water features taking the flow are the common reasons. If all of those check out, the flow switch or its wiring may have failed.
