Hayward HeatPro Flo/PS Error: Flow Switch & No Flow
Quick Summary
- Flo (HeatPro) or PS (Summit) means the water pressure switch is open — the heat pump does not sense adequate water flow through the heat exchanger.
- The most common causes are pump off, time clock in the off cycle, open bypass valve, or dirty filter — confirm water is actually flowing before testing the switch.
- To test the switch: disconnect the orange wires (HeatPro), run the pump, and check continuity at the switch terminals — not through the wires.
- After adjusting the switch, always cycle the pump off and confirm the heat pump shuts down — a switch set too sensitive can allow the heat pump to run without adequate cooling water.
What Flo/PS Means
The Flo or PS code indicates the water pressure switch located inside the heat pump's electrical panel is open. This switch is a safety device that prevents the heat pump from operating without water flow — running the compressor without water flow through the titanium heat exchanger would rapidly overheat the refrigerant and damage the compressor.
While the switch can fail on its own, the overwhelming majority of Flo/PS calls are water flow problems, not switch failures. Always confirm actual water flow before opening the electrical panel.
Step-by-Step Troubleshooting
Step 1: Verify the Pool Pump is Running
This is the first and simplest check. The HeatPro will not operate when the pool pump is off. Confirm the pump is running at the pool equipment pad — do not rely on the automation display alone.
- Check the pump time clock. If the pump is on a time clock, make sure the current time falls within the ON period.
- Verify the pump is actually moving water — listen for motor operation and check for return flow at the pool returns.
Step 2: Check Filter Pressure and Clean if Needed
A heavily loaded filter creates high head pressure that can reduce flow below the switch activation threshold. Check the filter gauge reading:
- If pressure is 8–10 PSI or more above the clean starting pressure, backwash or clean the filter.
- After cleaning, restart the heat pump and check if Flo/PS clears.
Step 3: Inspect All Valves and Bypass Lines
Open bypass valves on heat pump plumbing are a very common cause of Flo/PS. A bypass allows water to take the path of least resistance around the heat exchanger, resulting in little or no flow through the unit even though the pump is running at full capacity.
- Close all bypass valves on the heat pump supply and return lines.
- Confirm all suction-side and return-side valves are in the fully open position for filter mode.
Step 4: Test the Water Pressure Switch
Once you have confirmed the pump is running, filter is clean, and valves are correct, if Flo/PS persists the switch itself may need adjustment or replacement.
- Open the electrical panel of the HeatPro (power off at breaker first).
- Locate the water pressure switch — on HeatPro units it is wired with orange wires. Disconnect the orange wires from the switch terminals.
- Restore power and start the pool pump. Set your VOM to the ohms/continuity position.
- With the pump running and all bypasses closed, check for continuity directly at the switch terminals — not through the disconnected wires.
- If there is no continuity (switch open), try adjusting the switch: turn the thumbscrew counterclockwise 1 full turn and retest.
- If there is still no continuity after adjustment, the switch is faulty — replace it.
Critical Safety Check After Adjustment
Any time you adjust the water pressure switch, you must verify it still cuts off the heat pump when water flow stops. After adjusting, reconnect the wires and run the heat pump normally. Then turn off the pool pump and confirm the heat pump shuts down within a few seconds due to Flo/PS. If the heat pump does not shut down on loss of flow, the switch has been set too sensitive in the wrong direction and must be readjusted.
Step 5: Check Wiring to the Control Board
If the switch tests closed (good continuity) with the pump running and full flow, but Flo/PS is still displayed:
- Inspect the orange wires from the switch to the control board for any breaks, pinching, or corrosion at connectors.
- If wiring is intact, the control board is misreading the switch signal — replace the control board.
Frequently Asked Questions
The heat pump shows Flo/PS only at night. Why?
This is almost always a time clock issue. The pool pump timer is set to run during the day but turns off at night, and the heat pump's thermostat is still calling for heat after dark. Program the heat pump run schedule to overlap completely with the pump run schedule, or configure the automation to prevent the heat pump from calling for heat when the pump is off.
Can I run the heat pump on low speed with a variable speed pump?
Possibly not. The HeatPro requires a minimum of 30 GPM. Many variable speed pumps running at low RPM do not deliver adequate flow. If you are using a VS pump, ensure it is running at a speed that delivers at least 30 GPM when the heat pump is active. Most installers set a dedicated heat pump speed on the VS pump schedule.
The pressure switch adjustment did not hold — it keeps drifting. What next?
A switch that cannot hold a stable setting after adjustment has a worn mechanism — the internal diaphragm or spring is fatigued. Replace the switch rather than continuing to adjust it. A marginal switch may pass Flo/PS intermittently but allow the heat pump to run with insufficient flow during fluctuating conditions.
Why does the manual say to check continuity at the switch, not through the wires?
Because a break anywhere in the wire from the switch to the control board mimics an open switch. Testing at the switch terminals directly isolates whether the switch itself is the problem. If you test through the wires and get no continuity, you cannot distinguish between a bad switch and a broken wire. Always test at the switch first, then trace the wiring separately.
Is the HeatPro pressure switch the same part as the Summit?
The switch function is the same, but they are wired differently — HeatPro uses orange wires, Summit uses purple wires. When sourcing a replacement, confirm compatibility with the specific model. Always disconnect the wires before testing continuity to avoid feedback from the control circuit affecting your reading.