By-passing High Limit Switch on Pentair MasterTemp 400 Heater

wwtennant

Gold Supporter
Mar 21, 2015
32
Bellaire/TX
If HLS is functioning properly then it says water is getting to 135. That means you have inadequate water flow through the hear exchanger and what little water is flowing through is over heating.

Lack of scale on SWG has no correlation to scale in the heater. If heat exchanger tubes are restricting water flow then water will overheat in heater.
But the flow of water into the spa is very strong like it always has been and the pressure is not running abnormally high. Restricted water flow would seem to me like it would affect both of those... no??
 

wwtennant

Gold Supporter
Mar 21, 2015
32
Bellaire/TX
Do you have an external bypass?

Maybe it's the internal bypass. If you look in the Inlet, you should be able to see the half of the internal bypass with the spring. If you look in the hole where the thermal regulator goes, you should be able to see the other part of the internal bypass with round disk.

Do you have a picture of the system?
I will have to check tomorrow when there is daylight. I will take a picture as well and post.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,526
Northern NJ
But the flow of water into the spa is very strong like it always has been and the pressure is not running abnormally high. Restricted water flow would seem to me like it would affect both of those... no??
No, there is a manifold bypass that will divert the rest of the water not going through the heat exchanger. The hot water will mix with the bypassed water and look normal at the spa.

 

wwtennant

Gold Supporter
Mar 21, 2015
32
Bellaire/TX
No, there is a manifold bypass that will divert the rest of the water not going through the heat exchanger. The hot water will mix with the bypassed water and look normal at the spa.

Am I wrong in thinking that if what you described was occurring that the hot water that mixes with the bypassed water would be warm but not the normal 105 or so that comes into the spa when it operates normally?? The reason that I ask is that the water is the normal "hot" water if the heater is running, it is not below normal which makes me feel it is not "mixed" if the heater is going. Does this make sense?? Just seems that if the flow was restricted and heater running that I would get the proper flow to the spa but not the proper heat due to the mixing?? I really appreciate the help... any thoughts?
 

JamesW

TFP Expert
Mar 2, 2011
16,521
The water should not be "hot" coming out of the heater. It should be a few degrees warmer, but not hot.

Check the internal bypass by looking into the inlet or the hole where the thermal regulator goes.
 

wwtennant

Gold Supporter
Mar 21, 2015
32
Bellaire/TX
The water should not be "hot" coming out of the heater. It should be a few degrees warmer, but not hot.

Check the internal bypass by looking into the inlet or the hole where the thermal regulator goes.
JamesW wins the prize... I looked into the thermal regulator hole but this time the head of my thermal regulator fell off of the spring and dropped down by the outlet pipe. Thus, I opened that to retrieve it and, surprise, surprise, I found not only the thermal regulator but the broken clip from the manual bypass. Thus, now confirmed that I need to replace that part.

Now, the question is whether that job is too much for me to handle. I am pretty handy but I watched the video that ajw22 posted above and this job looks like a 4 to 5 hour job with significant risk or really messing something up when either prying open the internal pieces / parts or when reinstalling all this and hoping there are no leaks.

I'd be curious if y'all would recommend that I take a shot at this myself or whether I should hire a pro for it. Any idea what that costs?? Is it a $150 job or $500 job?? Any and all thoughts are appreciated as they always are by me!! Y'all rock!!
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,526
Northern NJ
It has to be a half day job and cost a few hundred. You have a good description of the problem and should be able to call around and get some estimates.