Heater displays HLS and will not fire; may occur immediately on call for heat.

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

Open high-limit switch, Loose high-limit wiring, Overheating in heat exchanger, Scale buildup restricting flow

Safety First: Turn off power and gas. Allow the heater to cool before touching internal components.

Check wiring: Locate the high-limit switch on the water header. Ensure both wires are firmly attached and not damaged.
Reset (if manual): Some high-limit switches have a manual reset button. Press it once after the unit has cooled.
Verify flow and filter: Confirm adequate water flow and a clean filter to prevent overheating.
Replace switch: If HLS persists and overheating is not present, the high-limit switch may be faulty and should be replaced.

Medium 3/5

High Limit Switch

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