Spa Heater Issue

Kit

Well-known member
Mar 10, 2016
211
Medford, Oregon
I recently noticed that my Pentair MasterTemp heater is cycling on & off without reaching the set temperature. Also, when the heater cycles off, the "Service Heater" light goes on. Any idea what the issue might be? I admit that the heater has not been serviced since I bought it new about 4 1/2 years ago.

Thank you so much for your help.

Kit
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
24,668
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
That is a symptom of overheating due to low flow.

What is your clean filter PSI and current PSI?

Clean your filter.

What RPM is your pump running at?

Increase your pump speed.
 

Kit

Well-known member
Mar 10, 2016
211
Medford, Oregon
Thank you for the response. When the pump is running daily on the filtration cycle, I believe that the pump speed is 1,700rpms. Clean filter PSI is 8 & the current PSI is the same. When we are in the spa, we run the jets at 3,000rpms & the PSI is about 25. This is when we notice the heater cycling without reaching the set temperature of 98F. It is time to clean the filters. But as I mentioned, the pressure has not changed.
 

Kit

Well-known member
Mar 10, 2016
211
Medford, Oregon
I consulted my notes & apparently I had the same issue several years ago. The culprit was indeed the thermal regulator. So I think you might be on to the solution. So a few quick questions:

1. Where exactly is the thermal regulator located?
2. To verify that the thermal regulator is indeed faulty, am I correct in assuming that the HLS (high limit switch) LED will be illuminated when the Service Heater light is on?
3. If so, is the HLS LED located on the circuit board on the underside of the heater control panel?

Thank you for your help!
 

Kit

Well-known member
Mar 10, 2016
211
Medford, Oregon
Looks like I answered my own questions. Sorry for the confusion. But since many of you have a wealth of experience in these matters, I would appreciate your feedback on the following: In order to narrow down the culprit to the thermal regulator, my plan is to first determine if any of the diagnostic LEDs on the heater's circuit board are illuminated when the heater cycles off. I assume that if an LED is illuminated, the corresponding component is faulty & needs to be replaced. If none of the LEDs are illuminated, I plan to remove the thermal regulator & see whether it opens under hot water. If it does not, I plan to replace it. Does this sound like a reasonable approach? Thank you so much.
 
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Kit

Well-known member
Mar 10, 2016
211
Medford, Oregon
Update: I confirmed that the high limit switch LED was on while the heater was cycling on & off. Next I removed the inlet pipe & the disc against which the thermal regulator sits was in place. I looked into the thermal regulator housing & the internal bypass looked fine (i.e. not obviously broken). Finally, I immersed the thermal regulator in 170F water & it failed to open. Looks as if I need a new thermal regulator. Is my thinking correct? BTW, is it recommended to replace the spring & clip as well?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
24,668
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Yes, replace the entire thermal regulator assembly.