Troubleshooting a Spa That Isn't Heating

Follow this logical, step-by-step guide to efficiently diagnose a no-heat issue.

Step 1: Check the "Heat Demand" Light
First, locate the heat demand indicator. This light may be on the topside control panel or directly on the spa's circuit board.

If the light is ON: The control system is receiving all necessary signals (from temperature sensors, pressure switch, and flow switch). You can skip checking these components and proceed directly to diagnosing the heater's power path.

If the light is OFF: The issue is likely with an input signal (e.g., a faulty sensor, flow switch, or pressure switch). This guide focuses on when the heat demand light is on.

Step 2: Diagnose the Heater Power Path
When the heat demand light is on, the problem lies in the delivery of power to the heater.

Verify Incoming Power: Confirm that the spa is receiving the correct line voltage (typically 240V).

Check Voltage at the Heater Terminals: With the system calling for heat, carefully measure the voltage at the heater's terminals.

If voltage is missing or low: The issue is with the delivery circuit. The heater relay or the entire circuit board is likely faulty and needs replacement.

If full voltage (e.g., 240V) is present: Proceed to an amperage test.

Perform an Amperage Test: Use a clamp meter to check the current draw at the heater.

If amperage is present and correct: The heater is operating electrically. The issue may be a separate problem, such as a plumbing blockage preventing water from flowing through the heater.

If voltage is present but there is no amperage draw: The heater element is open (burned out) and the entire heater assembly must be replaced.

Reference: A standard 4 kW heater at 240V should draw approximately 16–17 Amps (Calculation: Amps = Watts / Volts).

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