Mastertemp 400 Heater

Mvaughan

Member
Apr 9, 2018
6
College Station, TX
My Mastertemp 400 heats up to about 83 degrees, the burner shuts off, the service heater light comes on, then it restarts. It continues this cycle until it reaches the desired temperature. I have replaced the thermoregulator and the HLS sensor. Not sure what else to do?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
26,578
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
The HLS is often caused by lack of sufficient water flow through the heat exchanger. This can be due to several things:
  • Thermal regulator not opening.
  • External bypass open.
  • Internal bypass broken.
  • Pump too small or on too low rpm.
  • Clogged filter.
  • Scale in heat exchanger.
Start by checking the thermal regulator or your filter pressure.

 
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Mvaughan

Member
Apr 9, 2018
6
College Station, TX
Thank you! I Think I found it. The internal bypass valve broke off. Found the piece stuck at my salt generator. Now Ill tackle this project next weekend!

Another quick question. I noticed my replaced HLS was leaking. I removed and re tephlon taped but it doesn't see to screw in tight. It will get snug and continue to turn. It doesn't look stripped, maybe the internal threads? I never over tightened. Should I replace it again?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
26,578
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I don't know what is going on with your HLS sensor. When I replaced mine it came wrapped in Teflon tape and screwed right in.

Did you get a genuine Pentair part? I have found the non Pentair replacement parts to be sketchy at times.
 

Mvaughan

Member
Apr 9, 2018
6
College Station, TX
I did, it was in Pentair packaging and pre-wrapped in Teflon tape... I'll get a better look at the threads in the manifold this weekend as I'm going to have to get in there to replace the internal bypass valve.
 

Mvaughan

Member
Apr 9, 2018
6
College Station, TX
Fixed the heater issue by replacing the internal bypass valve. It was pretty easy... but I cannot get the new HLS switch to tighten. I cleaned the inside of the port (had a lot of old Teflon tape in there). I re Teflon taped it and it still will not tighten all the way. It will get snug and then get easy. It's gotta be the threads inside. I tried to seaI the best I could but it still drips. Any suggestion on how to seal it up so it won't drip? should I try to re-thread the port? Looks like heavy plastic, may do more harm than good?
 

JamesW

TFP Expert
Mar 2, 2011
26,012
Sounds like you stripped the threads. You might need a new manifold.

You can drill and tap it one size bigger and then use a brass reducing bushing.
 

Pool Clown

In The Industry
Sep 5, 2008
2,191
Silicon Valley, CA
If there was alot of Teflon tape on there previously, I would suspect that this happened to the last person to replace it. Either a cross thread, or cracked threads. There isn't really much tape used at the factory, this is what leads me to believe that it has been replaced once already. I would clean the threads on the manifold and use Teflon paste. If it still leaks, take it out once more and clean the paste off as good as you can. If it is cracked, you may be able to better see if there is a crack. The Teflon paste will get into the crack and provide a good contrast..
 

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