Heater Scaling and Failed Thermoregulator: Jandy Jxi 400 NG with VF

[Myburneraccount]

Hello everyone.

Have had a Jandy JXi 400NG with versaflo installed for about a year. Recently had very loud banging/knocking occurring when the gas heater ignited. My PB has come by to service the heater and said that 1) the thermoregulator had failed and 2) there was a large amount of scale present on the manifold backing plate.

I use the PoolMath app to keep my water chemistry in line along with a tfp test kit and digital pH meter. My TA is around 110 and my pH rises to about 8.0-8.2 by the weekend when I service the pool. I usually add enough acid to drop the pH back down to 7.3-7.4. Over the last month, I've been testing every other week due to travel but each time the pH is no higher than 8.2.

What could cause the large amount of scaling on my pool heater? Is it really the pH that could cause the issue? My CSI has always been in the acceptable range. Could the failed regulator have caused a rise in temperature/CSI or did the scaling lead to the failed regulator?

Most of the scale appears to have been surface level and the PB has cleared away what was reachable and is replacing the thermoregulator.

I am hoping to understand what led to this so that I can prevent the issue going forward. My usual pool routine is every weekend except for the past 4 weeks. Should I be monitoring pH 2x week?




After picking away scale.

 

[PoolGate]

That for sure looks like very incorrect water balance. Post a full set of tests including CH. What test kit are you using?

 

[1poolman1]

Hello everyone.

Have had a Jandy JXi 400NG with versaflo installed for about a year. Recently had very loud banging/knocking occurring when the gas heater ignited. My PB has come by to service the heater and said that 1) the thermoregulator had failed and 2) there was a large amount of scale present on the manifold backing plate.

I use the PoolMath app to keep my water chemistry in line along with a tfp test kit and digital pH meter. My TA is around 110 and my pH rises to about 8.0-8.2 by the weekend when I service the pool. I usually add enough acid to drop the pH back down to 7.3-7.4. Over the last month, I've been testing every other week due to travel but each time the pH is no higher than 8.2.

What could cause the large amount of scaling on my pool heater? Is it really the pH that could cause the issue? My CSI has always been in the acceptable range. Could the failed regulator have caused a rise in temperature/CSI or did the scaling lead to the failed regulator?

Most of the scale appears to have been surface level and the PB has cleared away what was reachable and is replacing the thermoregulator.

I am hoping to understand what led to this so that I can prevent the issue going forward. My usual pool routine is every weekend except for the past 4 weeks. Should I be monitoring pH 2x week?

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After picking away scale.

Is acid being added through the skimmer? Amazing that the regulator is so corroded and the copper of the heat exchanger not.

 

[JamesW]

Do you have a tab feeder?

 

[Myburneraccount]

That for sure looks like very incorrect water balance. Post a full set of tests including CH. What test kit are you using?

I use pool math and tftest kit. Is my pool math log not syncing?

Of note, I typically log results, add chems (don’t always log acid addition), and don’t retest after adding suggested amount. I also don’t always log the addition even though I always add acid following testing. That’s why my log always shows ph around 8-8.2.

Calcium is 450.

Is acid being added through the skimmer? Amazing that the regulator is so corroded and the copper of the heat exchanger not.

No it’s being added in the pool in front of the return.

The only time any acid has been added in the skimmer is CYA. Once by the PB’s worker that added so much he had to pull the filter and backwash (got it confused with calcium) and once by me to raise at the beginning of summer.

my PB is telling me this is related to pH as all other metrics are in line. Could the hot water from the spa use cause the CSI to spike leading to the scaling?

Really at a loss to what I did wrong here. TA was at 90 most of the summer except the last couple weeks when I was traveling it’s risen to 110.

 

[Myburneraccount]

Do you have a tab feeder?

No pool is SW with a truclear system. Can you please expand on what you are thinking around this?

 

[1poolman1]

No pool is SW with a truclear system. Can you please expand on what you are thinking around this?

Inline or off-line tablet feeder. They can easily cause that kind of damage. Not sure about the scale.

 

[Myburneraccount]

That for sure looks like very incorrect water balance. Post a full set of tests including CH. What test kit are you using?

https://troublefreepool.com/mypool/DJBK3k6

 

[Myburneraccount]

Inline or off-line tablet feeder. They can easily cause that kind of damage. Not sure about the scale.

Is the thermoregulator damage likely related to the scaling?

 

[1poolman1]

Is the thermoregulator damage likely related to the scaling?

Very bad chemistry.

 

[JoyfulNoise]

The scale is most definitely uncontrolled calcium scaling from high CSI. Your CSI might be ok in the bulk water but it’s not ok inside the heater tubes. In the heat exchanger tubes the water is closer to 140°F or more. So with a CH of 450, TA of 110 and pH at 8.2, your CSI is off the charts positive (> +1.0). That means calcium is going to scale like crazy inside the tubes. You can see the calcium scale inside the tubes. The heat exchanger needs to be descaled before going back into service. There are videos online for doing that.

As for the UG corrosion, hard to say. If the boiler scaled up the entire header block may have gotten too hot and that caused excessive corrosion of the UG. In any case, you should check the system bonding to make sure that the heater’s bonding lug is wired to the other equipment bonding. A broken bonding wire could drive galvanic corrosion.

 

[JamesW]

Can you show the system?

 

[Myburneraccount]

Can you show the system?

Yes can take pics tomorrow during the day. Anything specific you would like to see?

 

[Myburneraccount]

The scale is most definitely uncontrolled calcium scaling from high CSI. Your CSI might be ok in the bulk water but it’s not ok inside the heater tubes. In the heat exchanger tubes the water is closer to 140°F or more. So with a CH of 450, TA of 110 and pH at 8.2, your CSI is off the charts positive (> +1.0). That means calcium is going to scale like crazy inside the tubes. You can see the calcium scale inside the tubes. The heat exchanger needs to be descaled before going back into service. There are videos online for doing that.

As for the UG corrosion, hard to say. If the boiler scaled up the entire header block may have gotten too hot and that caused excessive corrosion of the UG. In any case, you should check the system bonding to make sure that the heater’s bonding lug is wired to the other equipment bonding. A broken bonding wire could drive galvanic corrosion.

That makes sense. I have a versaflow bypass so the only time water goes through the system is when the heater is on. Aside from the chemistry, any downside from the lack of ambient water flowing through after spa use?

TA is only recently at 110 since I’ve been out of town for the past month (servicing intervals at 2 weeks instead of 1 week). I drop acid once a week, could the few days that the pool rises to 8pH really cause that much scaling?

How can I prevent this in the future? Lower CH? Never allow pH to rise above 7.8? I’ve had the heater for less than a year and can’t say I’ve used it more than 20x total. Just trying to figure out if this is only a chemistry issue (which I can control or something more in the system.

Forgive my ignorance but what is the UG?

 

[Myburneraccount]

I wanted to update this thread in case someone else runs into the same issue. I had two failed thermoregulators in rather short time while obsessively maintaining pH in the ideal range. This led me to look for other possibilities and found that the bond wire to the heater was very loose and a lot of components were not properly bonded. Not sure how everything got past inspections but upon properly bonding all equipment, I'm please to say I've had no further issues. The issue was most likely galvanic corrosion and for good measure I have added a sacrificial anode to the loop. No corrosion on the anode since bonding and going a year strong without any issues.