I had been dealing with an ""HL"" error for weeks. The heater would shut down, sometimes the pump wouldn't run, or it would run for hours but the tub wouldn't get up to temp. On the advice of tech support I readjusted the pressure switch, purged for air bubbles, and even replaced the pressure switch, all with no effect. Finally, thinking that a High Limit error might have something to do with the high limit temp sensor, I replaced it. Immediate satisfaction! Once up to temp, the pump and heater only run a couple of minutes to maintain proper temp.what a relief to have a spa that finally works! I'd been advised that ""these sensors seldom fail"", but apparently some do. It was a cheap and quick repair that didn't even require draining the tub or closing service valves.