Lochinvar Flow Interlock Missing or Bypassed

Heater display shows normal operation but pool pump is off; heater may attempt to fire without flow.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Pressure switch jumpered, Incorrect wiring of flow switch, Failed pressure switch stuck closed

Safety: Operating a heater without water flow can destroy the heat exchanger and create a fire hazard. Turn off power immediately.

Steps:

Inspect pressure switch wiring: Ensure the water pressure switch is wired correctly and not permanently jumpered. Remove any unauthorized jumpers.
Test switch: With pump off, the pressure switch should be open (no continuity). If it reads closed, it is stuck and must be replaced.

Do not operate the heater until a proper flow interlock is restored.

Hard 4/5

Water Pressure Switch

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