Heater displays HLS and shuts down; may restart after cooling.

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

Overheating due to low flow, Failed high limit switch, Scale buildup in heat exchanger, Blocked internal water passages

Safety first: Turn off power and allow heater to cool.

Check system flow: Confirm pump speed, valve positions, and filter condition. Correct any flow restrictions.
Inspect high limit: Locate the high limit switch on the header. Check for loose wires or corrosion. Replace if the switch is open at normal temperatures.
Descale if needed: If the heater is older and HLS trips frequently, have a professional inspect for scale and perform chemical descaling or replace the heat exchanger.

Medium 3/5

High Limit Switch

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