Jandy JXi CHECK FLOW: Water Pressure Switch Troubleshooting

What CHECK FLOW Means

The JXi uses an internal water pressure switch to verify that enough water is flowing through the heat exchanger before allowing the burner to fire. When the switch is open, the control board displays CHECK FLOW and will not attempt ignition.

This is a critical safety feature. Firing the burner without adequate water flow would overheat the heat exchanger, potentially cracking it or triggering the high limit switch. The pressure switch must close before the ignition sequence begins.

Unlike some error codes that require a manual reset, CHECK FLOW will auto-clear as soon as the pressure switch detects sufficient flow. If you restore flow and the heater fires normally, the problem was purely hydraulic.

Step-by-Step Troubleshooting

Owner-Level Checks

Verify pump operation

1. Confirm the filter pump is running and fully primed. Look at return jets for strong, steady flow.
2. If the pump is on a timer or automation system, verify the schedule has the pump running when the heater is called.
3. Check that the pump is not air-locked or losing prime.

Check for flow restrictions

1. Empty the skimmer basket and pump strainer basket.
2. Check the filter pressure gauge. If pressure is significantly above your clean baseline, clean or backwash the filter.
3. Make sure all suction and return valves are fully open, especially any valve between the heater and the pool return.
4. Remove any winterizing plugs that may have been left in place.

Check variable speed pump settings

1. All JXi models require a minimum of 30 GPM. Many variable speed pumps at their lowest energy-saving speed do not produce 30 GPM.
2. Program a dedicated heater speed into the pump or automation system that produces at least 30 GPM.
3. If the pump is connected to Jandy AquaLink or iAquaLink, verify the pump speed relay or RS-485 command ramps the pump speed before calling for heat.

Tech-Level Checks

Test the pressure switch directly

1. With the pump running at full speed and adequate flow confirmed, locate the pressure switch on the heater header.
2. Disconnect the two wires from the switch and check continuity with a multimeter. With flow present, the switch should be closed (near zero ohms). Without flow, it should be open.
3. If the switch stays open even with strong flow, it may need adjustment or replacement.

Adjust the pressure switch

1. The JXi pressure switch is adjustable and factory-set to 7 psi. If the switch is not closing with adequate flow, the set point may need to be lowered slightly.
2. With your fingers, turn the adjustment sprocket very slowly clockwise until the heater goes off.
3. Then slowly turn the pressure switch adjustment sprocket counterclockwise one-quarter turn. Setting it too low defeats the safety protection.
4. If the switch requires significant adjustment to close with good flow, replace it instead.

Inspect the internal bypass

1. The JXi internal header bypass regulates flow through the heat exchanger. If it is stuck or incorrectly adjusted, flow may not reach the pressure switch threshold.
2. Inspect the bypass for debris, corrosion, or a stuck valve. If the optional VersaFlo accessory (JXIVFKIT) is installed, inspect it as well.
3. Clean or replace as needed and retest.

Check for air locks

1. Air trapped in the heat exchanger can prevent the pressure switch from closing.
2. Open the drain plug on the heat exchanger header briefly to bleed trapped air.
3. This is especially common after pump service, filter cleaning, or seasonal startup.

Common Parts That Fix This Problem

• Water pressure switch
• Internal bypass valve assembly (or optional VersaFlo kit JXIVFKIT)
• Heat exchanger drain plug and O-ring (for bleeding air)
• Filter cartridge or DE grids (if flow restriction is at the filter)
• Pump impeller or diffuser (if pump output has degraded)

How to Prevent CHECK FLOW From Coming Back

• Maintain clean filters so flow stays above 30 GPM during heater operation.
• Program variable speed pumps to run at adequate speed during heater calls.
• Keep suction and return valves fully open when the heater is expected to run.
• Bleed air from the heat exchanger after any plumbing work or pump service.
• Inspect the internal bypass annually during pre-season startup.