Cause of rusted heater?

[cmcq]

The insides of my 5-6 year old Pentair MiniMax NT gas heater just rusted out. I re-plumbed to skip the heater so we can still use the pool, but I curious about what would be the major cause for this - having a SWG or having pH running a little high much of the time? pH has been a little bit of a battle for me. I haven't had a chance this week to collect/post my pool chemistry, but even if pH were high for the last month or so, would that be enough time to rust through or is this a longer term problem?

I'll probably ask for heater recommendations at some time in the future but if there is a better time to get one (fall vs spring), I'd appreciate knowing that too

22k gallon IG, SWG

Thanks
Charlie

[chem geek]

Charlie,

It is low pH, not high pH, that accelerates rusting. Significantly elevated chlorine levels can accelerate corrosion, so a pool using chlorine with no CYA in the water (such as many indoor pools) would be at greater risk. If your heat exchanger in your heater is made of copper, then the rusting is most likely accelerated by the higher salt levels in the pool that are required to operate the saltwater chlorine generator (SWCG). When you get a replacement heater, get one that is more chemically resistant such as cupro-nickel or titanium. One can also use a sacrificial anode (usually made of zinc) buried in moist soil and connected to the bonding wire in order to reduce the rate of metal corrosion.

Richard

[Pool Clown]

Did the rust cause the leak? Or did the leak cause the rust? Anything the water touches (in the heater) shouldn't rust. Most everything in that heater is plastic or copper. But if the heater developed a leak, then the rust began, and, well, you know what happens then.

My guess is that the heater developed a leak (unrelated to rusting) then the rust was/is a product of the leak. Sometimes if the heater ran especially hot for long periods then cooled then hot again, the expanding and contracting can cause the transitions (from the copper exchanger to the plastic header) leak, but those kinds of environments are normally seen in commercial applications.

Note: I don't see many Mini Max NT's. But on this and other forums, I've noticed that those heaters in particular are not too popular.

Best time to get a heater? Just before you need one.

[Searcher]

The insides of my 5-6 year old Pentair MiniMax NT gas heater just rusted out.

This calls for a lot more investigation as to what exactly happened.

There should be nothing inside the heater to "rust" which means we are using the common name for iron or steel reacting to oxygen in the water which shows as the delightful orange stains we have all seen.

Since there should be no ferric substances in any pool piping; what could have rusted? As noted in a prior post, we may be dealing with a chicken and egg scenario whereas a leak somewhere attacked the shell of the heater which caused the rust you are seeing.

Since no units are perfect and since no light commercial pipe is truly tested for proper thickness with these units, a leak in a copper coil may have developed due to improper bending and/or annealing of said pipes or from using a lighter gauge pipe like type m where type L or thicker should have been used. As I said, this pipe is used to create the coil"s" that the pool water circulates through.

I have seen this happen with coils on heat pumps that carried r-22 refrigerant which is not close to being as corrosive as pool water. It was simply a bad batch of pipe that Trane bought to make their coils. The coils were replaced by Trane less the labour to replaced said coils and with that, this is why I would investigate where the leak originates.

Why all the bother?

If it is a small section of a coil it can be replaced for a nominal fee and you again have a working heater for little cost.

If an Iron pipe nipple was used where a brass nipple should have been used, same procedure; replace the nipple with a brass nipple and off you go.

Lastly, you may have recourse with Pentair to at least get a replacement coil.

So out with the tools and please let us know what you find inside the unit.

[chem geek]

Perhaps he meant "corroded" rather than rusted. Copper can corrode producing green to blue to black substances.

The key would be determining if the corrosion was from inside the pipe going out or from the outside of the pipe going in -- something that could be seen by examining the section of pipe that failed. The former would be corrosion from the pool water while the latter would be corrosion from condensation in the heater.

[Searcher]

Perhaps he meant "corroded" rather than rusted. Copper can corrode producing green to blue to black substances.

The key would be determining if the corrosion was from inside the pipe going out or from the outside of the pipe going in -- something that could be seen by examining the section of pipe that failed. The former would be corrosion from the pool water while the latter would be corrosion from condensation in the heater.

Yup, as a plumber there is a huge difference to us between rust and corrosion.

My thoughts still stand re a possible minor pipe section replacement compared to replacing a whole heater.

If it did fail after 6 years, they must have use something like 15 to 17 gauge pipe which is thinner than the "DWV" drainage copper, we used to use or perhaps a section popped open which is not uncommon with cheap, thin pipe.

Wow could I tell stories about the wrong pipe being used in certain applications.

[PoolDoc]

The insides of my 5-6 year old Pentair MiniMax NT gas heater just rusted out. I re-plumbed to skip the heater so we can still use the pool, but I curious about what would be the major cause for this - having a SWG or having pH running a little high much of the time? pH has been a little bit of a battle for me. I haven't had a chance this week to collect/post my pool chemistry, but even if pH were high for the last month or so, would that be enough time to rust through or is this a longer term problem?

Hi Charlie;

I'm both a plumber and a pool guy, so I could follow what all the folks were saying, but I'm not sure it made sense to you.

'Rust' is orange brown corrosion that happens to iron or steel. Copper corrodes, but doesn't exactly rust. Did you mean "rust" precisely, or did you mean "corroded and started leaking"?

I've seen heaters fail all sorts of ways.

They are mostly made of steel and iron, with the copper heat exchanger making up only a small part of the heater bulk. If you store chlorine like trichlor, or muriatic acid near a heater, the fumes can destroy a heater from inside the combustion chamber causing both rust and other types of corrosion. I've seen heaters reduced to a dangerous crumbling mess this way. A leaky container of damp trichlor will destroy any heater it's near, and pretty quickly, too.

On the other hand, if it's corrosion within the water pathway, low pH (not high) can destroy the copper heat exchanger. Putting trichlor (acidic!) tabs in the skimmer, on a pool with a heater, is a common way to kill heaters.

Probably, you do almost as much damage by putting an SWCG upstream of a heater, so that the freshly chlorinated water, complete with tiny but very corrosive amounts of undissolved chlorine gas, might eat a all-copper heat exchanger. I haven't seen this personally, but I'm guessing it happens.

And, then there's salt. Salt facilitates almost all types of metal corrosion. If you had excessive levels of salt, or a SWCG that took high levels, that might have caused the problem. I haven't checked Pentair's site, but my recollection is that your heater is NOT salt rated.

If you tell me a bit more, I can probably offer more focused information. But, I'll be tied up this weekend, so I probably won't respond again before Tuesday.

Ben
"PoolDoc"

[Pool Clown]

After reading this post again, i noticed that "a leak" was never reported. Just that the heater "rusted out". Yes, the poster mentioned that he took it out of the plumbing, but maybe because it was unsafe? My guess here, as Richard suggested, may be condensation.

Maybe the OP could chime back in here, and tell if the heater was leaking or not, how bad was it leaking, and maybe even describe where it was leaking from (if possible).

[cmcq]

Thanks for all the replies. For some reason I didn't get notified when they were posted.

Anyway, here is what I know and what I don't.

When I open the heater, all the metal parts I see are rusted. The pan on the bottom, the outside of the gas line, some of the sheet metal that seems to house the pipes and heater mechanism, etc. I don't know if the rust was caused by water than leaked out of the plumbing/heater, or another source (rain?). Given how widespread it is across the inside of the unit, it would have to be a lot of water but some of it could have come after the big leak which was causing the pool to lose pressure.

In the past few years, I've had problems with metal stains in the water and had to consistently put metal binding agent in the water and/or the vitamin C treatment. Since the heater has been removed, I haven't had any issues with metal stains. If it is related, that could indicate some issues inside the pipes, right?

I can't pinpoint the leak that led to the final demise of the plumber.

Thanks to PoolDoc's comment, I located the Pentair manual and it says clearly "These heaters are designed for the heating of swimming pools and spas, and should never be used as space heating boilers, general purpose water heaters, in non-stationary installations, or for the heating of SALT WATER." I'm going contact the miserable, greedy, lousy pool company who installed it and go back at them (although I have very low expectations with that).

Assuming that does nothing for me, I'm getting estimates on new heaters. One is the RayPak - Digital Pool Heater P-R406A-EN-C Natural Gas, and the other is an un-named Hayward heater (I'm getting the details next week). Both quotes are around $3100 - ouch. Based on chem geek's suggestion, it appears I should ask for the cupro-nickel or titanium, which I suspect will drive the price up further.

Any final thoughts from the group (and thanks again)
Charlie

[Pool Clown]

A Layer of rust throughout, as you describe, suggests that the rust may have come from chems stored in close proximity to the heater (in the same room).
Or...
A pin hole leak that acted like a mister, and kept the area in question not so much wet, but humid.

The absence of metal stains after you removed the heater suggests a possible chemistry problem.

Raypak heaters are great heaters IMO, i think you will be happy if you choose them.