Cal Spas FLOW Error — Flow Switch Fault Fix

What Does This Error Mean?

FLOW means the flow switch on the heater isn't seeing water flow — the system disables heating to prevent dry firing.
Most often it's a clogged filter, low water level, or air-locked pump.
Check water level (above filter intake), pull and rinse the filter, and confirm valves are open.
FLOW clears once water is flowing past the switch.

Affected Models

Cal Spas Patio Series
Cal Spas Hawaii
Cal Spas Genesis
Cal Spas Atlantic Series

Common Causes

Filter cartridge clogged
Water level below skimmer intake
Closed or partially closed valve
Pump air-locked after recent water change
Flow switch failed (rare)

How to Fix It

Check water level.

Open the cover.
Water should be above the skimmer intake but below the highest jets/headrests.
If low, fill with a hose to the proper level.
Low water is the most common FLOW cause — pump can't circulate without water above the intake.
Pull and rinse the filter.

Open the filter compartment.
Remove the cartridge.
Rinse with a garden hose, working from inside outward to flush debris from the pleats.
For heavy buildup, soak overnight in spa filter cleaner.
Reinstall.
Check valves.

Walk around the equipment area (open access panel on the side of the spa).
Look at the valves on the plumbing.
All should be in OPEN position (handle parallel to the pipe).
Closed valves prevent flow regardless of pump operation.
Bleed the pump.

If you recently drained and refilled, air can be trapped.
Loosen the pump union slightly until water trickles out (catch with towel), then retighten.
This bleeds air.
Restart the spa — pump should prime and water flow.
Restart and watch.

Power off at the breaker for 30 seconds, then on.
Pump should run and FLOW should clear within 1-2 minutes.
If FLOW persists, the flow switch may have failed (40–80 USD part).
Service-tech replacement is straightforward.

Frequently Asked Questions

How often should the filter be cleaned?

Rinse with a hose: every 2-4 weeks for typical use.
Deep clean (overnight chemical soak): every 3 months.
Replace cartridge: every 1-2 years.
Heavy use, lots of swimmers, or older spas need more frequent cleaning.
A clean filter prevents most FLOW errors.

Will FLOW damage anything?

If you ignore it and run the spa anyway, yes — the heater can fire dry and burn out (200–400 USD heater replacement).
Cal Spas' protection prevents this by disabling heat when FLOW is active.
Don't bypass the protection.
Fix the cause.