Safety: Turn off power to the heater before accessing the control compartment.

Steps:

Locate outlet sensor: On Lochinvar pool heaters, the outlet water temperature sensor is typically threaded into the outlet header or manifold.
Inspect wiring: Check the sensor leads for cuts, abrasions, or rodent damage. Ensure the connector at the control board is fully seated and free of corrosion.
Check sensor resistance: With power off and wires disconnected, measure resistance across the sensor with a multimeter. Compare to the temperature/resistance chart in the service manual. A reading of infinite (open) or near zero (short) indicates a bad sensor.
Replace if faulty: If readings are out of range, replace the outlet temperature sensor with the correct Lochinvar part number for your model. Use thread sealant approved for potable water and do not overtighten.

If a known-good sensor still produces E07, the control board may be defective and should be evaluated by a technician.

Display shows E07; heater does not fire and may indicate an issue with the outlet water temperature sensor.

Possible Causes