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Flow Errors (FLO / FL / Flow Switch Problems)

Flow Error Diagnostics (FLO / FL / Flow / Pressure Switch Problems)

Flow errors occur when the spa control system detects that water is not moving properly through the heater. Most spa packs monitor water flow using either a flow switch, pressure switch, or M7 sensors.

Common flow-related error codes include:

• FLO – Flow switch open
• FL – Flow problem detected
• FL1 / FL2 – Flow switch or pressure switch issue
• DR / DRY – Heater dry condition
• OH – Overheat caused by restricted flow

Step 1 – Check the Filter

The most common cause of a flow error is a clogged or dirty filter.

• Remove the filter
• Restart the spa
• If the error disappears, the filter needs cleaning or replacement. 

Note: Another possibility if the error goes away after removing the filters is a build up of material like leaves in the front suction side of the pump causing slower water movement exacerbated by the filter being in place. 

Step 2 – Check Water Level

Low water levels can cause air to enter the plumbing system.

Make sure the water level is high enough to fully cover the skimmer opening.

Step 3 – Check the Circulation Pump

Many modern spas use a small circulation pump to constantly move water through the heater.

If the circulation pump fails, the spa may show a flow error.

Signs of a failed circulation pump include:

• No water movement
• Spa not heating
• Pump humming but not pumping
• No sound from the pump

Step 4 – Check for Air Lock

After draining and refilling a spa, air can become trapped in the plumbing.

• Loosen the pump union slightly
• Allow trapped air to escape
• Retighten the union

This often restores normal water flow.

Step 5 – Inspect the Flow or Pressure Switch

Older spas often use a pressure switch or flow switch to confirm water movement.

Common issues include:

• Stuck switch (Switch Stuck Open or Closed)
• Switch Open (Has good water pressure but note closed)

Measure across the two terminals on a Pressure or flow switch with a meter using ohms. The read does not matter, only continuity. If there is continuity with the pump, the switch is bad. If there is no continuity with the pump on and moving water with good pressure the switch is bad. Replace the switch in either case. You can test the system to see if it would work normally if the switch was working by jumping the two wires together but only after the pump is on. If you do it before many systems will not heat because it looks for the switch to be open when the pump is off. If the switch shows closed that can create a code as well. This prevents you from just tying the wires together and bypassing this important safety feature. 

Step 6 – Check for Plumbing Restrictions

Flow problems can also be caused by restrictions in the plumbing system.

Check for:

• Closed slice valves (Slice valves with no keepers can vibrate closed) 

           Note: If you do not have slice keeper add them)

• Collapsed or stopped up filter cartridges
• Blocked suction fittings (This alone will not do it. It would have to be the filters and Suction Stopped up at the same time)
• Debris in the pump impeller

Note: If you ever remove the filters to clean them, power down first. If you don’t and there are any items floating in the tub they can be pulled into the front suction side of the pump. I have seen many things pulled into the pumps like bikini bottoms and more.

Important Electrical Parts Notice

Always diagnose the spa system properly before replacing parts.

Electrical components cannot be returned once installed.

Call for basic support or parts help or Text pictures for part identification.

Call 1-866-829-3660 or Text Parts Pics to 772-800-5445 Know Before You Go.

Hot Tub FLO Error Troubleshooting | Flow Switch Problems