Show us some pix of the equipment pad.
What are you using to lower the pH?

Most exchangers are designed to withstand up to 6k in salinity. I doubt the SWG is the issue. I'll take a shot a blame a poorly installed tablet feeder that is siphoning back into the exchanger. That is the typical cause but you would think Hayward would have picked that up after the first failure.

IF they are adding muratic or bisulfate through a skimmer, that could do it too.

Jandy claims their heaters are rated to 6k in salinity.

If they didn't chlormatic, I'd bet they'd void their warranties if salt was used.

Make sure you have a chemical resistent check valve between the salt cell and heater. The check valve will keep gases from the salt cell from getting into the exchanger and ruining it. We have had some exchangers fail on salt pools. so far since installing the chemical resistant check valve we have not had any repeat offenders.

A couple of updates:
The installed gas line from the meter to the heater is currently 1 inch. The installation guidelines for a 400k heater call for it to be 1.25 inches. Everybody missed that. Would that cause heat exchange failures? Hayward technical manager wants me to replace the gas line. We are using Muriatic acid to lower the PH. WE pour it into the deep end. I'm not aware of a chemical resistant check valve installed either.

Are all the bond wires tied to the same ground? They should be. Verify that there is no stray voltage by checking with a volt meter from the house's main ground to the heater, pump, etc. with all devices running and when turned off.

Additional Information:

The Chemical resistant check valve is installed. I didn't know what it looked like. I also included links pad site pictures. Hayward cover the repair under warranty, they just want me to upgrade the gas line to 1.25 inches.

Here is a link that might be useful: Pad Site Pictures

I have had the same heater and SWG going on 3 1/2 years now without any issue.

It is probably one of the problems mentioned above, either chemistry or electrical currents.

I doubt that the gas line would have any impact other than flame outs if it were too small. That shouldn't affect corrosion though.

Can you post what your PH, TA, CH & salt levels are usually at? How far do you let them deviate over the course of the year?

Also, check to make sure the heater is properly grounded. I think I can see the wire attached to the side of the unit but you need to do a continuity check to ground to make sure.

Also, I do not have a check valve between the SWG and heater but when the pump is off, the water tends to drain in the other direction towards the returns.

The photos help. The link is missing the h in http though.

Whoever plumbed this was incompetent. 1st 90 after the heater is too close to the heater. The check valve should have come before the TurboCell. The valve directing return water isn't centered,The return lines are not evenly spaced and too high off the ground. The lack of extra pipe between fitting is not conducive to repairs.

Recommendations: Starting from the return side of the heater, extend that line about a foot then drop the line to the pad with the 1st 90. Then a stub and the check valve and another stub and then the TurboCell. Dig up the return lines at the pad and make them evenly spaced. Move the pool sweep ine to the other side of the return lines to be cloer to the booster pump. I hope they used flex as it will make this easier. Replumb as needed to make it look neat. Don't reuse the valve. Use clear glue. Looks nicer. Blue is really for underground plumbing where moisture contact is more prevalent.

Check for stray voltage as I mentioned in my earlier post.

This should cure the heater core issues and make your equipment pad less of an eyesore.

The 90 being too close to the heater is not an issue. The check valve that you see is not for protecting the heater, but to keep the spa from draining (odd way to do it teeing off the pool like like that). The Tee valve not being centered is splitting hairs, and it's elevation is insignificant.

I won't let people use clear glue above grade, because it's easy to forget joints. I expect people that do the pipe assembly do a nice neat job with a gray glue. But a clean job looks good regardless of the color of glue used. People tend to overuse clear glue have it run all over the pipes.

I think you are silly to suggest that they "Dig up the return lines at the pad and make them evenly spaced." This is incredibly not an issue, while being a pet peeve of your's nobody else really cares.

Besides the easiest way to resolve this it to tip the tee valve vertically and then looping it over to the right line.

I digress.....

Hayward does not require a check valve between the heater, and Salt cell. A salt cell only generates about 2-3 ppm at average flow rate (some commercial units more). So when the pump turns off, there isn't and incredibly high concentration of chlorine in the cell unless the flow switch is stuck closed and continues to create chlorine while the pump is off.

Personally, I would have to examine the exchanger and look at the erosion, or corrosion to make a better determination. Your Hayward rep should be capable of making this diagnosis.

If the spa is raised, the shown check valve is correct ly placed.The spa has a pool return in it which would siphon off water thru that return to eith the pool's water level or until the water level in the spa drops below the return and lets air in.

If the heater core shows erosion, the internal bypass in the heater is malfunctioning.

The amount of pipe after the heater does matter. The water in the pipe will sink the heat that remains in the event the heater doesn't get a cool down cycle, like in a power failure.

Pet peeve or not, it's ugly and doesn't allow for future service. Home owners paid a good deal of money. Why shouldn't they accept it done neatly versus the it works mentality?

Good techs wipe any excess glue off.

Given the number of heat exchanger failures this forum member has experienced, stray voltage is my #1 guess. It may be coming from either a noisy ground or the cell.

"The amount of pipe after the heater does matter. The water in the pipe will sink the heat that remains in the event the heater doesn't get a cool down cycle, like in a power failure."

When heaters had firebrick Heatsinks were essential. Since heaters now have insulation, or sometimes nothing. (master temp). They do not retain as much heat as they used to.

"Pet peeve or not, it's ugly and doesn't allow for future service. "

Yes, but why replace it after the fact. Make it right when is requires attention.

Would the 1 inch gas line contributed to the Heat Exchange failures? The installation calls for a gas line of 1.25 inches

Not ones that will cause it to leak.

The salt cell was replaced in the middle of the Summer. Bottom Line is Hayward Technical Manager is telling me it's the 1 inch gas line that's the problem. He insists that the heat exchanger is sooting up. They won't authorize repair until the gas line is repaired. The builder is balking at me asking him to pay to install the correct gas line.

What size heater is it, and how many feet is the gas line.

I would also ask Hayward, how a sooting exchanger would cause leaking.

400k BTU heater roughly 8-10 feet of gas line. Flex tube at the heat side. Please explain Leaking? Hayward's theory is that a 1 inch gas line does not deliver the correct volume to the heater. This incorrect volume is causing the heater to burn incorrectly and soot up. I looked at the vent fan and don't notice any soot.

In the last 16 years I’ve been repairing and replacing pool heaters in the Houston area, we’ve encountered that issue thousands of times. Your salt is definitely the issue regardless if the heat exchanger is cupronickel or copper. In our environment we have to keep our salt generators at 60 percent chlorine out put regularly and 100 percent 1 day week. Two things salt destroys, Natural Stone and metal. We didn’t have this issue in our Industry until the late 90s when builders installed chemical feeders or salt chlorine generators on every equipment Pad. It’s the same issue with all major brands and not just Hayward. But copper and Cupronickel haven’t changed in the last 20 years, so why is this all of a sudden an issue? Why are heaters from the 80s and even 70s with the same metal alloys lasting this long? It all goes back to our ignorance as an industry? We finally realized the problem in the mid - late 2000s when the only thing that changed was chemical feeders. Even if installed on the discharge side of the heater, every time you empty the pump basket, your causing what’s known as “back pressure” Injecting air in the system causing water to backflow and sit directly inside the heat exchanger. If you have a d.e filter and have ever noticed a bunch of d.e appearing out of nowhere around your main drain, same issue. The solution is simple , an all plastic(impervious to hydrogen gas released from salt cell or extremely corrosive tablets that are 99 percent tricolor) prevents the water from backflowing and rotting out your heater. If a checkvalve is present but is the tradition clear glass jandy checkvalve with a metal spring is used...... no good. Remember salt is good for “us and the environment “ Not good for natural stone that is not polished and or sealed nor any types of Metal. You also need to make sure the heater is properly bonded with an 8-10 guage solid copper wire at the external binding lug. This has nothing to do and is seperate from grounding. This prevents galvanic corrosion in thinner metals by bonding iron rebar in pool structure and all metal in equipment area to a galvanized Steele grounding rod that draws electrons evenly through all metal ( known as the bonding grid) your pool company and Hayward should have informed you of these issues from the original Install which has been common knowledge in our industry since 2011.

I am curious did you ever get the heat exchanger issue fixed? I am facing the same problem with my heater and salt water pool, heat exchanger #4 just arrived, I am scared to put it in.I am thinking of converting the pool to chlorine system

This is not a salt issue solely. Your calcium hardness levels, pH levels and total alkalinity levels are elevated and have been for a long period time. Because salt systems inherently drive pH and alkalinity levels up during operation, it's important to control these levels with additions of acid. A sequestering added on a weekly basis, will aid in controlling scale.

Another probable issue is too little water flow through the heater. Proper water flow won't allow scale to form.

I replaced a heat exchanger on a indoor pool about 20 years ago. Salt systems were not available at that time. The exchanger was completely blocked. Turns out major scale on the plaster finish also. All from elevated calcium, pH and alkalinity levels.

I've seen these occurrences even 30+ years ago.

Test your tap/fill water also for your pool. You'd be surprised what your putting into your pool, and your water glasses.