Pentair Mastertemp 400 copper tube corrosion... how much time do I have left?

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cymertony

Member
Jul 17, 2014
6
San Marcos/CA
Pool/spa heater in our salt pool is a over 9 years old and I just took the manifold off for just the second time in it's life (thermostat/internal bypass replacement), but I see that the bottom left tube end is quite corroded. I feel like there's enough left to clean up and put a new o-ring on, but wondering how much longer you folks think this will hang on? One or two years? Heater is only used for the spa but is piped in for both (no bypass).

Thinking I should start saving for a new heater, don't think I'd be inclined to replace the tube sheet on a >10yr old heater. So far the only repairs have been an internal bypass at around 4yrs old, and a flue sensor last year, so hardly any maintenance needed to date. However, things seem pretty rode hard in there so I would just replace the whole thing.

Thoughts from the community? Am I overthinking it?

Will look to see if I have pictures from the first internal bypass replacement.

Thanks,
Tony

Equipment: 25k gal inground pool/spa, IC40 salt cell, Intelliflow VS, De filter, Mastertemp 400
 

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Welcome to TFP.

How have you chlorinated your pool the last 10 years?

What test kit do you use?

Can you post your water chemistry in the format..

FC
CC
pH
TA
CH
CYA
SALT
Water temperature

All that goes into answering how long the heater may last.
 
Did you use sandpaper on these tubes?

Copper should build a patina over time and the color should go from a bright shiny “Copper” color to a dull brown color like going from a new penny to and old brown penny.

This is due to a film of oxidized copper compounds that provide a protective layer.

The layer protects from further oxidation because the copper is already oxidized.

The lack of a brown patina usually indicates an exposure to acidic conditions that dissolve the copper patina and expose elemental copper to oxidation.

img_6368-jpg.522007


img_6366-jpg.522006
 
Copper comes in the elemental state with an oxidation state of 0.

It can be oxidized to +1 or +2 by losing one or two electrons.

If the water chemistry is good, the oxidized copper will form compounds that bond to the elemental copper and provide a protective barrier to further oxidation.

If the water chemistry is bad, the protective layer will not form and the copper will continue to oxidize.

Acid by itself does not corrode copper.

Acid just prevents the oxidized copper compounds from forming on the copper.

The corrosion comes from the oxidizers in the water like dissolved oxygen, ozone, hydrogen peroxide, chlorine or bromine.

Electron Configuration for Cu, Cu+, and Cu2+ (Copper and Copper Ions)

1s2 2s2 2p6 3s2 3p6 3d10 4s1

1s2 2s2 2p6 3s2 3p6 3d10 4s0

1s2 2s2 2p6 3s2 3p6 3d9 4s0



Copper-Electron-Configuration.png
 
cymertony said:
Pool/spa heater in our salt pool is a over 9 years old and I just took the manifold off for just the second time in it's life
Click to expand...
What did it look like the first time?

You can see the correct brown color at the base where the O-rings go and the water did not get to the copper.

Above the O-ring is corroded and this indicates bad water chemistry; probably a nearby tab feeder or a zero TA.

The damage is probably recent as the copper would have been completely destroyed if the chemistry was this bad for 9 years.

What has changed recently?

1691956324657.png
 
cymertony said:
Pool/spa heater in our salt pool is a over 9 years old and I just took the manifold off for just the second time in it's life (thermostat/internal bypass replacement), but I see that the bottom left tube end is quite corroded. I feel like there's enough left to clean up and put a new o-ring on, but wondering how much longer you folks think this will hang on? One or two years? Heater is only used for the spa but is piped in for both (no bypass).

Thinking I should start saving for a new heater, don't think I'd be inclined to replace the tube sheet on a >10yr old heater. So far the only repairs have been an internal bypass at around 4yrs old, and a flue sensor last year, so hardly any maintenance needed to date. However, things seem pretty rode hard in there so I would just replace the whole thing.

Thoughts from the community? Am I overthinking it?

Will look to see if I have pictures from the first internal bypass replacement.

Thanks,
Tony

Equipment: 25k gal inground pool/spa, IC40 salt cell, Intelliflow VS, De filter, Mastertemp 400
Click to expand...
Put some new O rings on, watch your chemistry (inline tab feeder?), and start saving.
 
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Sorry forgot that it's good to have some background info on the pool.

BTW, love all the patina talk! Yes, before I took the picture I had cleaned the copper ends to help remove buildup at the base that might prevent the new orings from seating well. At the 4yr mark when I pulled the manifold they were patina'd green but this time I they were a dull brown. Dang I shouldn't have cleaned them but couldn't help myself... I know better, err

Chemistry-wise, I was a die-hard TFP chemistry follower for the first couple years then slowly realized the only thing that was varying was pH so I slacked a bit in recent years, but always check FC. I use the TF100 kit with speedstir and sample sizer. Recently took measurements but not all:
  • FC - currently 6 but I typically don't do anything extra if it's between 4-10 using DPD test. Been using liquid chlorine a lot more in the past 6 months, finally realized my IC40 had been dying, but only after it actually died and I came home from vacation to a green pool (light green!... but green nonetheless)
  • CC - Was always 0 so I stopped checking... it's been awhile
  • pH - I shoot for 7.5 but if it's above 7.2 and looks below 7.8 using a white background I don't usually correct.
  • TA - stopped checking years ago since it always tracked with pH, might be time for a check.
  • CH - always 400 here so I stopped checking a while ago
  • CYA - 70ish (that eyeball at the bottom plays tricks on my vision, now I know why the range is 60-80). I check CYA a few times a year or if my FC is not maintaining.
  • SALT - 3800ish, use to test regularly but now I just follow the reading from the IC40 and check it every once in a while using the drop test. Isn't silver nitrate just the best thing ever for your skin :)
  • Water temperature - currently about 85 (San Diego)
The only chemicals that go in my pool are HCL and liquid chlorine (31.5%) although the chlorine gets old so I buy it when I need it. Also I buy and add pool salt and CYA when necessary.

Is the salt responsible for the pitting? The copper ends were definitely not pitted last time I was in there... but it was 5yrs ago. Maybe I need to be more vigilant about checking for CC.

Appreciate the expertise from the team, it's been awhile for me and I didn't expect such quick responses
Tony
 

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All of my flow goes through the heater, but I keep flow as low as possible... just enough to keep the pool cleaner running properly. Usually 1800-2000 rpm on our intelliflo pump, depending on how long it's been since I cleaned or backwashed the filter.

Heater is all buttoned up again but still have my original problem, will open a new thread for that issue. I'm sure the community will have some insight on my issue.

Thanks all!
Tony
 
Last edited:
Sort of long story, but should be amusing, I'll do my best to recount for others to learn from, see the critical mistakes below (and I know better... that's the kicker):
  • Heater was cycling on and off due to HLS opening.
  • Removed and tested the HLS which was good (opening at 135F). Re-installed into manifold.
  • Removed and tested the thermal regulator and it was bad (Pentair model, last replaced five years ago).
  • Ordered the ARU part from Amazon because I could get it in one day.... (I know, I know.... )
  • Did a quick test on the new regulator with hot water and it opened so I installed it
  • Still getting HLS so not sure if maybe flow was low so checked flue temp but it was good... 260F if I remember?
  • Raised pump flow anyway, in steps, but still getting HLS. Check spa flow using spillway and jets, all have strong flow, check valves are open wide.
  • Pulled the manifold to check the internal bypass (can't check in place due to piping locations), the bypass broke as soon as I pushed it open.. probably was not broken until I touched it... who knows
  • Cleaned (oops) and inspected the copper ends of the heat exchanger.... saw pitting and wondered how much longer they might last... posted to forum about it.
  • Ordered new internal bypass, new manifold gasket and O-rings. Also, ordered new thermistor since it was the original one and a bit corroded. Not too bad, though, really.
  • Pulled and tested the AGS. All good. Opened at 140-145 I think?
  • Received parts, reassembled manifold, and installed onto heater. I installed thermal regulator prior to re-installing manifold onto heater. Anyone know why Pentair wants the regulator installed after manifold install? Seemed easier that way.
  • Still getting HLS. Wife starting to doubt my capabilities... Disassembled our front-load washer, cleaned seal boot, and re-assembled to appease her.
  • Pulled newly installed ARU thermal regulator to check opening point. Regulator not opening at 120F, 130F. 140F.... not opening until water temp raised to 160F! Errrrrrrrrrrrrr I previously checked quickly with hot water but didn't verify at 120F. HLS opens at 135F so opening at 160F is not much help. Requested refund from Amazon... with prejudice. Refund app didn't seemed bothered and just issued refund but I felt better.

  • This last bullet is for all the forum gurus who get so frustrated saying the same thing over and over.
  • Ordered PENTAIR thermal regulator and will test properly prior to installing.
Hope everyone enjoys and uses my case to help others.

Thanks,
Tony
San Diego, CA
 

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Pentair thermostat came in this past Wednesday and it tested perfect. I installed it immediately but just got around to testing it.

Heater turned on and ran perfectly until it heated the spa to the set temperature then shutoff as expected. It took 25minutes to raise the spa temp from 83 to 99. That seems ok to me... the spa is about 900 gallons if I remember correctly, air temp was 95F.

Thanks for your help and the help I got from reading about other peoples heater issues.

Tony
 
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