Can I fix Hayward code LO myself?

Start with these safe checks: Make sure the pump is running and fast enough. Turn the pump off at the breaker, empty the baskets and clean the filter (release pressure first), then check the valves are open. If flow is good and LO stays, call a qualified tech. Never bypass a safety switch.

When should I call a technician for code LO?

If flow is good and LO stays, call a qualified tech. Never bypass a safety switch. Smell gas? Leave right away, don't touch light switches or phones inside, and call your gas utility or 911 from outside. Never open a gas valve, burner, gas line, vent or flue connection, or bypass a safety switch. Repeated lockouts, scorching, soot, or a CO alarm mean shut it off and call a licensed gas technician.

Hayward Pool Heater Error Code LO: Pressure, vent or limit switch…

What LO means

A fault on the water pressure switch, vent pressure switch or temperature limit switch. It's not a low-temperature reading.

Likely causes

Low water flow
Dirty filter
Closed valves
Switch fault

Safe first checks

Make sure the pump is running and fast enough.
Turn the pump off at the breaker, empty the baskets and clean the filter (release pressure first), then check the valves are open.

When to stop

If flow is good and LO stays, call a qualified tech. Never bypass a safety switch.

Parts that may help

Only order a part once the checks above point to it, and match the part number to your model.

Pressure Switch - Adjustable, SPST-NO, 4010P$36.99

Checked against: Hayward Universal H-Series heater troubleshooting guide (UHS16b): diagnostic codes. Codes can differ by model and year, so confirm with your owner's manual.