Hot Tub & Spa Circuit Board Problems: Symptoms, Causes, and Fixes

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 or some buttons don’t work?
• Why don’t the spa-side buttons respond?
• Why are power connections burned or melted?
• Helpful tips most spa owners are never told

Introduction:

Hot tub circuit board problems can cause 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. It will help you understand what your spa is doing and why, so you can make the right repair decision with confidence.

Why will my 220-volt spa not heat?

Start by checking the topside control panel.

Is the heat indicator light on?

If the heat light IS on

1. Measure voltage across the two hot wires from the house (~220V expected).
2. If no 220V: the GFCI breaker or incoming power may be the problem.
3. If 220V is present: measure voltage at the heater terminals.

• 220V present at heater, but no heat → heating element is defective.
• No voltage at heater → circuit board is defective.

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If the heat light is NOT on

If error messages or blinking dots appear, 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 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 (low voltage, safe to touch).

• Heat light turns on → pressure switch or cable is defective.
• Heat light stays off → circuit board is defective.

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What do error codes or blinking dots mean?

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

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

Confirm water flow before testing to avoid damaging the heater.

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Why does my GFCI trip when heating or turning on?

Most GFCI trips are caused by a shorted heating element.

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

If the GFCI no longer trips → replace the heating element.

If it still trips, unplug one component at a time. When the GFCI stops tripping, the last unplugged component is faulty.

If all components are unplugged and the GFCI still trips, the circuit board transformer may be defective.

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Why does my pump turn on by itself?

Usually caused by a faulty topside control. Unplug the topside control—if the problem stops, replace it.

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

Moisture damage inside the topside control usually causes this. Replace the topside control.

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Why is the display acting strangely or some buttons don’t work?

Most often caused by a failing topside control; sometimes due to a defective circuit board.

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Why don’t the spa-side buttons respond?

Most often caused by a defective topside control. Check cables for damage or rodent chewing.

Diagnostic tip: unplug the topside control. Within one minute, the circulation pump should start. If not, check voltage and fuses with a meter.

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Why are power connections burned or melted?

This includes:

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

Loose connections cause resistance and heat, which burns components. Not a manufacturer defect.

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Helpful tips most spa owners are never told

• Burned heater connections 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.