What Does This Error Mean?

A Hayward flow switch fault means the heater or salt chlorinator is not detecting sufficient water flow through the unit. The most common cause is a dirty filter raising system pressure and reducing flow below the switch threshold. Backwash or clean the filter and ensure the pump basket is clear.

Affected Models

Hayward H-Series Heater
Hayward HeatPro Heat Pump
Hayward AquaRite Salt System
Hayward Universal H-Series
All Hayward heaters and salt systems

Common Causes

Dirty filter cartridge or sand filter reducing flow below threshold
Pump basket clogged with debris
Pump impeller partially blocked
Flow switch paddle stuck in closed position from scale or debris
Air in the suction line reducing pump prime and flow rate

How to Fix It

Check and clean the filter.

A clogged filter is the most common flow fault cause. For cartridge filters: remove and rinse the cartridge. For sand filters: backwash until the sight glass runs clear. For DE filters: backwash and add fresh DE. After cleaning, run the pump and see if the flow fault clears.
Check and empty the pump strainer basket.

A full pump strainer basket restricts suction-side flow significantly. Turn off the pump, open the strainer lid, and remove all debris from the basket. Also check the skimmer baskets at the pool wall.
Check that all valves are open.

A partially closed isolation valve on the suction or return line will reduce flow enough to trigger a flow switch fault. Trace the plumbing from the pool to the heater/salt cell and confirm every valve is in the fully open position.
Inspect the flow switch paddle.

The flow switch is a paddle-style sensor in the plumbing line. If calcium scale or debris has lodged around the paddle, it can stick in the closed (no-flow) position even when water is flowing. Isolate the flow switch, remove it, and check that the paddle moves freely.
Test flow rate at the return jets.

A simple flow test: hold your hand near a return jet in the pool. A strong jet confirms adequate flow — if the fault then persists, the flow switch itself is faulty. A weak jet confirms a flow problem — continue diagnosing the filtration system.

When to Call a Professional

If flow is confirmed strong (water moves well through the system) and the fault persists, the flow switch paddle or its magnetic reed switch may be stuck or failed and needs replacement.