Hayward AquaRite 900 "No Flow" Light On: Causes and Fixes

What the "No Flow" Light Actually Means

Inside the AquaRite 900 there is no actual flow sensor. Instead the unit relies on an external paddle style flow switch installed in the return line. The control reads the position of that switch. If it reports "no flow," the control will not energize the cell and the No Flow LED will either flash during a short start up delay or stay solid when it has decided flow is not adequate.

This is a safety feature that protects the cell from running without proper cooling and prevents gas buildup in dead headed plumbing. Any time this light is on, the Generating light will be off.

Step-by-Step Troubleshooting

Owner-Level Checks

Verify basic circulation

1. Confirm the filter pump is running and primed.
2. Look at the return jets. If they are weak or barely moving, treat this as a circulation problem first.
3. Check valve positions to be sure you are not pulling only from a nearly closed line.

Check filter and baskets

1. Empty skimmer and pump baskets.
2. Compare filter pressure to your clean baseline. If it is significantly higher, clean or backwash the filter.
3. After cleaning, restart the pump and watch the AquaRite for the start up delay. The No Flow light will usually flash for up to a minute before either going out or staying solid.

Inspect the flow switch location

1. Find the gray hex tee in the return line where the sensor is installed.
2. Make sure there is a decent length of straight pipe upstream. The system calls for roughly a foot of straight run before the switch. If the cell is upstream, it can count as straight pipe.
3. Check that the molded arrow on top of the hex body points in the direction of water flow.

Check the cable and plug

1. Trace the cable from the switch back to the control box.
2. Verify it is firmly plugged into the jack on the bottom of the enclosure.
3. Look for any obvious damage to the cable insulation.

Tech-Level Checks

If the hydraulics and plumbing look reasonable but the No Flow light stays on:

Rule out air and low speed limitations

1. With a two speed or variable speed pump, temporarily run the pump at full speed.
2. Bleed air from the filter using the air relief.
3. See if the No Flow light clears on high speed but not on low. If so, you may simply be running too slow to satisfy the switch.

Test the flow switch electrically

1. With power off, unplug the flow switch from the control.
2. Use a multimeter on continuity or resistance across the switch leads.
3. With flow present, the switch should show closed contact. Without flow, it should be open. If it never changes state or is intermittent, replace the switch.

Temporarily bypass for diagnosis only

Some techs will briefly simulate a closed switch at the board to determine whether the light clears. If you do this, make absolutely sure the pump is running and restore the proper wiring immediately after the test. Do not leave any bypass in place.

Evaluate plumbing changes

If the flow switch is installed immediately after a tight elbow, check valve, or heater outlet, consider re plumbing it to meet the straight pipe requirement.

Common Parts That Fix This Problem

• Replacement flow switch assembly with correct cable and connector
• Additional PVC fittings to add straight pipe upstream of the switch
• New pump impeller, motor, or filter media if underlying circulation is weak

Model-Specific Notes

• In some layouts the system allows the flow switch to be installed after the cell and to count the cell body as part of the straight run.
• On pool and spa combos, special plumbing configurations ensure the unit sees proper flow in both pool and spa spillover modes.

How to Prevent "No Flow" From Coming Back

• Keep the filter maintained so pressure stays close to the clean starting point.
• Avoid running variable speed pumps at extremely low RPM while expecting full chlorination.
• When re plumbing equipment, always leave room for straight pipe before the flow switch.
• Protect the cable from being pinched or damaged by other equipment.