Optimum Pool Technologies® High Limit Switch Compatible Replacement for Pentair MasterTemp & Max-E-Therm Heaters - Compatible Replacement for 42001-0063S

If you're buying this due to the Diagnostic LED on your Pentair stating it's the High Limit Switch, there is a very good possibility that it is actually a corroded Thermal Regulator, also located in the Manifold. My heater would heat on and off and was taking a long time to heat my spa. LED indicated it was the HLS. Bought this to replace, but heater still had the same issue and LED indicator. After exhaustive internet searches, I located lots of info stating that this issue is commonly due to a corroded Thermal Regulator. Sure enough, replacing it solved my problem and heater runs great now.

Worked perfectly. Even came with the tape dope already in place. Just had to Screw out the old + screw in the new.

My Pentair 400,000 Btu pool heater stopped running and gave me the "Service Heater" light on the control panel. The indicator light on the backside of the panel showed "HLS", meaning a problem with the High Level Switch part. After following the diagnostic tree in the manual (i.e. I knew I didn't have excessively hot water coming out as the heater never fired up) it was clear that the switch had gone bad. A few online videos showed that getting into the heater was pretty simple and replacing the sensor was a straight forward job. This switch proved a perfect "drop in" replacement for the original and, after a trip to the hardware store, I had my pool heater back in business. You can see the pictures for why I had to make a run to the store. The teeth on the outside of the sensor are for the wire clamps to slip on and make the connection. My original sensor's teeth had rusted so badly that they came apart when I tried to unplug and I could get the broken teeth out. Took the new sensor with me so I could test out and buy the right size connectors as I only wanted to make this drive one time. An 18mm wrench is the right size for removing/reinstalling the senor. Save yourself from the high prices of the pool store or an expensive repair call - this one is an easy DIY repair.

Excellent replacement. Worked very well for my Temp400

The switch fit and works just fine.

Danger: I just received two of these High Limit Switches from Amazon, and I tested them against Pentair's specification of 135 Deg. F for switching the pool heater off. They both failed to operate until dangerously high temperatures. One operated at 147.5 Deg. F, and the other operated at 145.3 Deg. F. Note that 3rd degree burns are near instantaneous if skin comes in contact with 145 Degree water. I believe Amazon should immediately suspend sales of this item, and Amazon and the manufacturer (a company call Optimum, NOT Pentair) should issue a recall of these devices, and contact the Consumer Product Safety Commission. This is a critical part of the safety system for the Pentair pool heater. I have access to laboratory grade thermal test equipment, including digital thermometers and a precision circulating water bath that I used in the testing. Each unit was tested multiple times, and the results were essentially identical. Most customers would not do this testing, and would think there were being protected by this switch. They would not be protected.

Working exactly as it should, no issues.

This high limit switch is much too small to fit my Pentair Mastertemp 400HD. I ordered the Thermistor and this High Limit Switch and both have the same thread size. I knew my Thermistor was bad and after replacing it the spa worked properly, but I could not replace the high limit switch because it’s the wrong size. The box the switch came in is marked correctly, but the part is not what the box says. There are 2 stickers on the box and it seems like it was marked wrong. I will be sending it back and looking for another vendor.