HL on a hot tub:
the high limit tripped.

What HL means

HL — HFL on some control packs — means the high-limit sensor cut power to the heater. That sensor sits at or near the heater element and exists for exactly one purpose: to stop the element cooking when the temperature there goes past a safe threshold. When you see HL, the safety device worked.

Why it is usually a flow problem

This is the part that surprises people. A tub can show HL while the water still feels barely warm, and the reason is that the high limit is not measuring the water you are sitting in — it is measuring the water at the element.

When flow is restricted, the small amount of water actually passing the heater gets very hot very quickly while the rest of the shell stays cool. The high limit trips on a genuine local temperature that never reaches the rest of the tub. So the fix is almost never "the sensor is bad." It is usually the same short list that causes a FLO error :

• A packed filter. Pull it out entirely and run the tub. If HL stops happening, that was it.
• Low water. Below the skimmer, the pump draws air and flow collapses.
• A closed valve left over from a previous repair.
• An air lock after a refill, where the pump is spinning air rather than moving water.

When it is not flow

• The high-limit sensor itself has failed. On many packs that reports as SN3 or SNB rather than HL, but a degraded sensor can trip early without failing outright.
• A failing circulation pump. Running, drawing power, not moving what it should.
• Scale on the element, which insulates it and lets the element surface run far hotter than the water around it. On well water this is a genuine and recurring cause — see our Howell page if that is your situation.

Do not just keep resetting it

A high limit that trips repeatedly is a heater being protected from something that has not gone away. Reset it once, check the four flow items, and if it trips again, leave it and call. The $185 service call covers the trip and the diagnosis, and you hear the fault and the cost before anything is replaced.

Where we stop

Electrical work on a spa circuit is licensed work in Michigan and Dr. Spa does not do it. We diagnose everything on the spa side of the disconnect, heater and sensors included, and tell you plainly which side the fault is on.

Related codes

FLO and FL1 , OH and OHH and DR and DRY all belong to the same family. The full error code index covers all twelve.