Hayward ProLogic Heater Not Firing

How the ProLogic Heater Circuit Works

The ProLogic uses a normally-open dry contact relay for each heater (up to two heaters supported). When the ProLogic calls for heat — based on the water temperature sensor reading versus the configured set point — it closes the dry contact. The heater then supplies its own low voltage (12–24VAC) through the bypass loop on terminal C. If the ProLogic's dry contact is closed and the heater is receiving that voltage back, the heater should fire.

This design means the ProLogic itself never supplies power to the heater — it only closes a low-voltage dry contact. If the heater does not fire, the issue could be on either side: the ProLogic is not closing the contact, or the heater is not responding to a properly closed contact.

Step-by-Step Troubleshooting

Owner-Level Checks

Step 6A: Confirm the filter pump is running

• Look at the local display and confirm the Filter LED is illuminated. The ProLogic will not activate the heater relay if the main circulation pump is not running.
• If the pump is not running and cannot be turned on, the pump circuit must be resolved first — see the Auxiliary Equipment Not Running article.
• If the pump is running, confirm the Heater LED status — is the Heater LED illuminated or dark?

Check heater set points

• Press Menu until "Settings Menu" appears. Navigate with (>) until the heater set point is displayed.
• Confirm the set point is above the current water temperature — the heater will not call for heat if the pool is already at or above the set point.
• The ProLogic factory default maximum pool temperature limit is 90°F (energy-saving mode). If the pool is at 89°F and the set point is 90°F, the heater may only run briefly. Raising the set point to 104°F during diagnosis eliminates this as a variable.

Check for Check System LED

• If the Check System LED is illuminated, navigate to the Default Menu to read the error. A water temperature sensor failure ("Wtr Sensor Short" or "Wtr Sensor Open") will prevent heating from operating.
• If a sensor error is present, see the Temperature Sensor Errors article before proceeding with heater diagnostics.

Tech-Level Checks

Step 6B: Verify the Heater LED status

• With the main circulation pump running, look at the local display. Is the Heater 1 (or Heater 2) LED illuminated?
• If the LED is NOT illuminated: the ProLogic is not calling for heat. This could be due to freeze protection being active, solar priority override, or the set point being below the current water temperature. Proceed to the service mode test.
• If the LED IS illuminated: the ProLogic is calling for heat but the heater is not responding. Proceed to Step 6D to test the heater relay.

Step 6C: Service mode test

• Press the Service Mode button on the local display. Service mode suspends all schedules, interlocks, freeze protection, and solar priority — it lets you manually force any relay on.
• With service mode active, press the Heater button to force the heater on.
• If the Heater LED illuminates AND the heater fires in service mode: the problem is a control-level issue (freeze protection active, solar priority overriding, schedule conflict, or interlock). Investigate those features in the Settings and Configuration menus.
• If the Heater LED illuminates in service mode but the heater still does not fire: proceed to Step 6D to test the dry contact relay.
• If the Heater LED does NOT illuminate in service mode either: replace the local display — the display is not generating the command signal.

Step 6D: Test the heater relay at terminal C

• With the Heater LED illuminated (in service mode if needed), locate the heater terminal block at position C on the main PCB — this is the dry contact output.
• Using a multimeter set to AC voltage, test the top terminal against ground. Then test the bottom terminal against ground.
• Expected reading: approximately 24VAC at each terminal (supplied by the heater through its bypass loop when the dry contact is closed).
• If both terminals show approximately 24VAC OR neither terminal shows 24VAC: proceed to Step 6E to troubleshoot the heater itself.
• If only ONE terminal shows 24VAC: the dry contact inside the ProLogic relay is not closing on both sides simultaneously — replace the main board (GLX-PCB-PRO).

Step 6E: Troubleshoot the heater side

• Confirm the heater has power — check the heater's own breaker and verify the heater display shows no error codes.
• Inspect each wire in the heater bypass loop for 24VAC. If voltage is present on both wires OR neither wire, either the heater has an internal error, the heater is not configured to bypass mode, or the heater is experiencing a failure — refer to the heater's own service manual.
• If only one bypass wire shows voltage, the bypass wires between the ProLogic and heater are likely damaged or wired incorrectly.
• Contact Hayward tech support at (908) 355-7995 if the heater is displaying its own error codes — this is outside the ProLogic's control loop.

Step 6F: Verify set points and solar priority after service mode test

• If the heater only fires in service mode, exit service mode and check whether freeze protection is currently active (water temperature near or below the freeze protection threshold).
• Check if solar heating is configured and currently active — solar priority prevents the gas heater from firing while solar is running.
• In the Settings Menu, confirm heater set points are at the desired temperature. Under the Configuration Menu, review whether the heater is set to "demand only" or "schedule" mode.

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