Mastertemp 400 Heater Incorrect Temp


New member
Jul 26, 2015
San Diego, CA
Loosing a battle to diagnose problem with Mastertemp 400 reading a temperature of about 10 degrees higher than actual. I've replaced the thermistor, thermal regulator, and today the logic board. I also cleaned the filter. Same issue. The heater shuts off at 103/104 high temp limit even though the actual water temperature is about 94 (what Intellitouch shows and water feels). No errors showing up. Not a gas flow issue because is runs fine until high limit hit. If I set high limit at heater to 95, it will shut off when it reads 95, although spa is actually only about 85.

-- Mark
Easytouch 8


TFP Expert
In The Industry
Jul 6, 2011
Get a thermometer and read the actual water temp. Automation systems can be wrong and so can how it feels. You can calibrate the temp sensor on the Intellitouch also if once you have tested the water temp with a thermometer and it is off.

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