Water boiling inside Hayward H400FDN Heater..??

[angelleye]

We just had a pool built which includes a Hayward H400FDN heater. Unfortunately, we're having problems with it right away.

When trying to heat up the spa to default setting of 104°F we're getting up to about 90°F when it starts making this awful noise and everything starts shaking as you can hear/see here: New video by Andrew Angell

It shuts itself down and displays a HS code on the screen, which apparently means "too hot". The info I'm finding is that the sound is water boiling in the heater, and the cause of this is usually water flow problems. However, when the heater doesn't have enough water flow/pressure, it shuts itself down with the LO message displayed. We're not getting that. Instead, we're getting the shutdown with HS code.

The plumber did come back to troubleshoot with me, and we made sure we're getting as much flow and pressure as possible and cranked the pump up nearly max. The waterfall, bubbler, etc. were looking great, but this did not solve the problem with the heater.

What confuses me is that the boiling point of water is 212°F. How in the heck is the water getting that hot inside the heater while the thermostat still reads less than 100°F?

Hoping that somebody in here can help me with how to troubleshoot this sort of thing when water flow does not seem to be the issue. Any information on this would be greatly appreciated. Thanks!

 

[vtpools]

Here's a link to the troubleshooting manual for your heater. I would check the bypass inside the heater manifold, it's noted on page 49 of the manual I linked. I saw one of these heaters do something very similar this past summer, and the issue was that the bypass valve had broken and got flushed out of the manifold. Basically there was enough water to trip the water pressure sensor, but most of it was bypassing the heat exchanger since the valve was gone and going back to the pool. The water that sat in the exchanger started to boil and caused an HS error. The weird thing is that it's happening at a certain temperature. Are you sure it's when it gets to 90ish or is it after a couple minutes?
Hopefully someone else can chime in, that's the first thing that came to my mind though.

 

[JoyfulNoise]

Can you post a slightly wider angle shot of the heater with all of the plumbing and the valve positions? It looks like you have a manual bypass in the plumbing and it’s important that the heater is getting the proper flow.

There is no flow switch in these heaters, only a pressure switch and it is possible to get enough pressure to trip the switch but still have insufficient flow. Also, these heaters operate in a high flow bypass configuration internally where only a small fraction of the water entering the heater actually flows through the heat exchanger. The hot water produced in the heat exchanger mixes with the colder water in the heater manifold and that produces the desired output water temperature. The combustion chamber is typical several hundred degrees Fahrenheit (around 300F or so) and so it is very easy for water to boil in the tubing at insufficient flow.

Since this is a new build, your pool builder should be tackling this issue. It is possible in a new pool build that debris got into the plumbing (especially if this is a gunite pool) and something got lodged into the heater manifold.

 

[vtpools]

Since this is a new build

Oops, missed that part. Disregard what I said, the issue I saw was on a heater that had been in use for a couple of seasons.

 

[angelleye]

Can you post a slightly wider angle shot of the heater with all of the plumbing and the valve positions? It looks like you have a manual bypass in the plumbing and it’s important that the heater is getting the proper flow.

There is no flow switch in these heaters, only a pressure switch and it is possible to get enough pressure to trip the switch but still have insufficient flow. Also, these heaters operate in a high flow bypass configuration internally where only a small fraction of the water entering the heater actually flows through the heat exchanger. The hot water produced in the heat exchanger mixes with the colder water in the heater manifold and that produces the desired output water temperature. The combustion chamber is typical several hundred degrees Fahrenheit (around 300F or so) and so it is very easy for water to boil in the tubing at insufficient flow.

Since this is a new build, your pool builder should be tackling this issue. It is possible in a new pool build that debris got into the plumbing (especially if this is a gunite pool) and something got lodged into the heater manifold.

So there is a bit of a story behind the plumbing. I was trying not to make my original post so lengthy.

When they first plumbed everything it was like this: Pool Plumbing and Equipment

I created the chart just to as a learning tool for myself, but upon doing so (and reading up on pump calibration) I realized this didn't seem quite "right" because I couldn't maintain pool temps while sanitizing at the same time.

After showing them this chart with my comments they came back and adjusted by moving the valve from in front of the heater to behind it, and then added a separate bypass valve, so it now looks like this: Pool Plumbing and Equipment - 2

That one was a little hard for me to diagram since there are are lots of options for which way to send water now...my color coding doesn't work as well, but hopefully you can get the idea. As pictured, all water flow is going through the heater, and my thought would be to use high pump speeds for a few hours per day to heat and clean the pool, and then run it at lower speeds the majority of the time.

This way seems more "right" than before, because now I can choose to send water through the heater and maintain pool temp while still sanitizing if I want, or I can bypass it entirely when we're simply not using it during summer months.

I never got a chance to heat up the spa on the original plumbing design, so I don't know if it would have been happening that way or not.

They've been back out again since I reported the heater problem, and plumber swears flow is not an issue at this point, but he didn't actually measure it with a flow meter, so I guess I'm just taking his word for it.

Does the plumbing look okay, or would you say this is likely the cause of the problem? If the plumbing seems like a potential cause of the problem, how can I push back logically? I worry they're just going to deal with Hayward and maybe get a replacement, but then we'll just have the same problem again if this plumbing is causing it, and I don't know how to verify for myself 100% that flow is not the problem.

 

[angelleye]

Here's a link to the troubleshooting manual for your heater. I would check the bypass inside the heater manifold, it's noted on page 49 of the manual I linked. I saw one of these heaters do something very similar this past summer, and the issue was that the bypass valve had broken and got flushed out of the manifold. Basically there was enough water to trip the water pressure sensor, but most of it was bypassing the heat exchanger since the valve was gone and going back to the pool. The water that sat in the exchanger started to boil and caused an HS error. The weird thing is that it's happening at a certain temperature. Are you sure it's when it gets to 90ish or is it after a couple minutes?
Hopefully someone else can chime in, that's the first thing that came to my mind though.

Yeah, I was able to run it for most of a whole day to get the pool up to 82 and didn't seem to have any issues there. It's only when trying to heat up the spa. I can get through the 80s without a problem, but when I get to 90 - 95 this starts happening.

 

[JoyfulNoise]

Your configuration is quite complicated but it appears that the valves are correctly plumbed. There's no need to put two valves on the heater as the same function can be had with one diverter valve on the input and one check valve on the output .... but you have what you have.

Here's a simple check - set the pump on a decent speed, doesn't have to be at full speed, but maybe 2800rpm or something like that. Make sure the valves are set so that all of the water is flowing through the heater and then water is returned to the pool at whatever returns are easiest for you to put your hand in front of. Make sure your sand filter is in FILTER mode and not bypass. Check the filter pressure when you do this and then walk over to your pool and put your hand in front of the return that is closet to the equipment pad. Does it feel like there's a strong flow of water coming out of the return? What pressure are you getting at the filter?

 

[1poolman1]

To add to JoyfulNoise comment, the last heater school I attended indicated that the actual combustion-chamber temperatures, in most modern heaters, are closer to 2K (yes, two thousand) degrees. I've seen heaters with soot-clogged heat exchangers actually melt the stainless steel internal part into puddles and then destroy themselves.

If there is not enough water flow to carry the heat away quickly the water will flash boil. That's why heaters bang and will actually jump off the ground at times, especially heaters like the JXi, Max-E-Therm, MasterTemp, that are quite lightweight for heaters. That steam pressure has to go somewhere, it can run locomotives.

 

[angelleye]

For those curious, they had some "eyeballs" in the spa that were small and pinching the water flow too much. They replaced those with some larger eyeballs and now the heater seems to be running smoothly.