Cause of rusted heater?

[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.