MasterTemp 400 Problem

Romoth

Silver Supporter
Sep 18, 2020
82
Houston, TX
Chlorine
Liquid Chlorine
Hi all, I have a problem with my mastertemp 400. It will heat up to lukewarm, but not heat up past that. I had a similar issue last year and had a repair person come out. I'm hoping to fix it myself this year. I was also concerned to see that there seems to be a lot of corrosion here. Any tips on next steps? Pictures below. Thank you in advance.
 

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Check the thermal regulator and bypass valve.


The lower bolts corroding indicates a possible heat exchanger leak. Remove the lower left bolt on the manifold. If water comes out, the heat exchanger is leaking.
 
Sorry for the stupid question, I can check both of those. when you say remove the lower left bolt, do I need the pool off for that, or should it be on?

If water comes out, does that mean I just bit the bullet and replace the whole thing, or is there a reasonable repair? Thank you!
 
One additional question, is what the heck could cause this? I have been over the top careful about my pool chemistry. In the entire time I've owned my pool, I've had to slam only twice. I've kept CSI within paramaters, etc.
 
Sorry for the stupid question, I can check both of those. when you say remove the lower left bolt, do I need the pool off for that, or should it be on?

Pool and pump off.

If water comes out, does that mean I just bit the bullet and replace the whole thing, or is there a reasonable repair? Thank you!
Heat exchanger parts can run $1500 - $2,000 if you do the labor.

New heater runs about $4,000.

 
How old is the pool and heater?

You the owner the entire time or did you inherit it?
 
Good news is no water out of bottom left bolt with pool off and pump off. Bad news is the bolt above it (second from the bottom left) is so corroded I can’t even get a nut on it to break it loose.
 
SLAM and CSI is not what affects a heater.

The heater needs at least an annual inspection to catch those problems earlier. It could be deteriorated O-rings on the tubes where they connect to the manifold leaking some water.