How to Fix / Troubleshooting

Safety: Turn off power before removing the control panel.

Steps:

Verify setpoint: Confirm the desired pool temperature is set correctly and that the heater is in Pool mode (not Spa, if separate).
Check external controls: If using an external pool automation system, ensure the control wiring to the Lochinvar heater is correct and that the external controller is calling for heat.
Inspect pool temperature sensor: Locate the remote pool sensor (if equipped) in the plumbing line. Check for secure mounting and intact wiring. Replace if corroded or physically damaged.
Test sensor resistance: Disconnect the sensor and measure resistance; compare to Lochinvar's chart. Replace if out of range.

If the sensor tests good but E09 persists, the main control board may need replacement by a qualified technician.

Display shows E09; heater does not respond to thermostat changes or shows erratic temperature readings.

Possible Causes