Pentair Mastertemp 400 takes forever to heat spa

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T

theface

New member
Dec 31, 2019
2
northern cali
hello all, I have a pentair mastertemp 400. Spa is in ground attached to the pool with a spillover. The service system light was on, i took off the front and the light switched back and forth between service heater/service system by the time I took off the top the PS light was on, but shut back off. I didn't do anything now no lights are on, but it still takes forever to heat, I've had it on for 2 hours and it went from 58-72. Outside temp is 59
 
Short cycling of the heater is usually caused by a bad thermal regulator or bypass valve. Or sometimes by a bad temperature thermistor.

What water temperature is being displayed on the heater control panel before it cycles off?
 
If the heater continues to run and not short cycle (repeated on/off operation), be sure your pool/spa isolation valves are closing the pool off completely. Slow heating is usually an indication that the suction valve is continuing to pull pool water into the spa line. You will see this as a constant overflow of the spa when it is running. They can get out of adjustment. Though that is rare, it does happen. Another issue is to be sure both valves are rotating when the spa is activated, one may have been turned off at the 3-way switch on the bottom (back?) of the actuator or may not be functioning.
 
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