Spa Troubleshooting Guide

Hot tub circuit board problems can cause a wide range of confusing symptoms—from no heat and error codes to pumps turning on by themselves or GFCI breakers tripping. This guide explains the most common circuit board–related issues, what causes them, and how to safely diagnose the problem before replacing parts. The goal is to help you understand what your spa is doing and why, so you can make the right repair decision with confidence.

Click a question below to jump directly to the answer

• Why will my 220-volt spa not heat?
• What do error codes or blinking dots mean?
• Why does my GFCI trip when heating or turning on?
• Why does my pump turn on by itself?
• Why does the wrong function turn on when I press a button?
• Why is the display acting strangely?
• Why don’t the spa-side buttons respond?
• Why are power connections burned or melted?
• Helpful tips most spa owners are never told

Why will my 220-volt spa not heat?

Start by looking at the topside control panel.

Is the heat indicator light on?

If the heat light IS on

This means the spa is calling for heat.

1. A technician should measure voltage across the two hot wires from the house. The reading should be about 220 volts.
2. If 220 volts is not present, the issue is usually the GFCI breaker or incoming power.
3. If 220 volts is present, voltage should be checked at the heater terminals.

• If 220 volts is present at the heater but the water does not warm, the heating element has failed.
• If there is no voltage at the heater, the circuit board is faulty.

If the heat light is NOT on

If you see error messages or blinking dots, see the error code section below. If no errors are displayed, the most common cause is a pressure switch problem.

Pressure switch test (if equipped)

1. Turn power to the spa off.
2. Unplug the pressure switch cable from the circuit board.
3. Restore power.
4. When the circulation pump starts, temporarily connect the two exposed pins.

• If the heat light turns on, the pressure switch or cable is defective.
• If the heat light stays off, the circuit board has failed.

Note: Not all spas use a pressure switch.

What do error codes or blinking dots mean?

Codes such as FLO, FL, or three blinking dots all indicate insufficient water flow through the heater.

Common causes include:

• Dirty or clogged filter
• Too many closed jets
• Debris in the pump
• Faulty pressure switch or cable
• Failed circuit board

Before testing anything, confirm that water is visibly moving in the spa. Never test the heater without confirmed water flow.

If water flow is confirmed, perform the pressure switch test described above. If bypassing the switch clears the error, replace the switch or cable. If not, the circuit board is the likely cause.

Why does my GFCI trip when heating or turning on?

The most common cause is a shorted heating element.

1. Disconnect the heater wires from the circuit board.
2. Restore power.

If the GFCI no longer trips, the heating element must be replaced.

If the GFCI still trips, unplug one component at a time, restoring power after each step. When the tripping stops, the last unplugged component is faulty.

If everything is unplugged and the GFCI still trips, the circuit board transformer may be defective.

On new installations, incorrect wiring is a very common cause of GFCI tripping.

Why does my pump turn on by itself?

This is almost always caused by a faulty topside control.

Unplug the topside control from the circuit board. If the problem stops, the topside control must be replaced.

Why does the wrong function turn on when I press a button?

This is usually caused by moisture damage inside the topside control.

The topside control should be replaced.

Why is the display acting strangely or only some buttons work?

In most cases, this indicates a failing topside control.

In rare cases, the circuit board processor or power driver may be failing.

Why don’t the spa-side buttons respond?

The most common cause is a defective topside control. Check the cable for damage, including rodent chewing.

Diagnostic check: Unplug the topside control. Within about one minute, the circulation pump should start automatically.

If it does not, verify incoming power and test all fuses with a meter.

Why are power connections burned or melted?

This includes:

• Main power terminal blocks
• Copper heater connections
• Relay and termination wiring

This damage is caused by loose electrical connections. Loose connections create resistance, which generates heat.

This type of damage is not considered a manufacturing defect and is not covered under warranty.

Helpful tips most spa owners are never told

• Burned heater connections after a board replacement are almost always caused by loose connections.
• Heater terminals should be tightened to 30–35 inch-pounds.
• Normal resistance readings at the circuit board do not indicate a short or failure.