Mastertemp 200 - 3 cracked manifolds!!

JamesW

TFP Expert
Mar 2, 2011
28,255
The problem with this bypass setup that he could very easily dead head the heater. He would need a three way diverter valve to avoid dead heading.
Possible.

In my opinion, all heaters should come with a flow switch for this exact reason.
 

JamesW

TFP Expert
Mar 2, 2011
28,255
Having the valves closed when the heater is on is about the only way that the pressure would build up enough to burst the manifold.

The water would boil and the pressure would go super high.

The hot water would reduce the strength of the plastic making it easier to crack.

I suspect that the heat exchanger might also be damaged.
 

wireform

Silver Supporter
In The Industry
Aug 15, 2017
3,122
Spring Valley, NY
Who is to say that there isn't another valve somewhere closer to the spa and they adjust it for what they would call a comfortable flow at the same time you have this heater running with not enough water flow. The water is cooked and not enough to absorb the heat, kaboom.
 

JamesW

TFP Expert
Mar 2, 2011
28,255
You really need to have the valves closed to be able to build up enough pressure to burst the manifold.

If the heater is not fully isolated, the pressure would not build up enough to burst the manifold.

You might see some melting or warping, but I suspect that the crack was due to full isolation.
 

JamesW

TFP Expert
Mar 2, 2011
28,255
If you close the valves while the pump is on, that will trap pressure in the heater.

So, even if you turn the pump off, the heater can still turn on.

In my opinion, the most likely explanation is that the heater ran while both valves were closed.
 

wireform

Silver Supporter
In The Industry
Aug 15, 2017
3,122
Spring Valley, NY
And he said it happened to another heater too so it can't be the heaters fault. Flat out human error. As you stated a flow switch may have saved the day.
 

JamesW

TFP Expert
Mar 2, 2011
28,255
The fact that it's outside would make it inconvenient to go outside to turn the heater off while doing any type of service.

It would also make it hard to notice that something was happening with the heater while you're inside working on the system.
 

JamesW

TFP Expert
Mar 2, 2011
28,255
The high limit and AGS sensors should shut off the heater when the water gets too hot but maybe not fast enough.

Maybe the high limit or AGS are not working correctly?

Check both to make sure that they are ok.

Freeze damage would do it if you have had any freezing weather.

Water hammer could possibly do it if a valve was slammed shut quickly while the water was flowing.

Overall, I think that the most likely answer is that the heater ran with the valves closed.
 

MSchutzer

Silver Supporter
Jan 15, 2021
161
Redwood City, Ca
Pool Size
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Surface
Plaster
Chlorine
Liquid Chlorine
Here’s another possible thought. What is the access path like to the heater‘s control panel? Is there any chance that your guests are stepping on the PVC pipes that connect to heater’s header?

They look like they are slightly elevated off the ground and in front of the heaters control panel. The PVC pipe is probably more flexible than the header, if the pipes were stepped on maybe the stress was transferred to the header.

It seems unlikely, but your problem is unusual.

Mark
 
Last edited:

JamesW

TFP Expert
Mar 2, 2011
28,255
If someone stepped on the plumbing, that could possibly be a cause of the cracks.

Maybe put something under the pipe for support.
 

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alleycats

Member
Mar 16, 2021
21
Antigua, Guatemala
The problem with this bypass setup that he could very easily dead head the heater. He would need a three way diverter valve to avoid dead heading.
Thanks. I'm not familiar with what you are describing. Can you think of any resource where I might find a picture or description of what you are describing.
 

alleycats

Member
Mar 16, 2021
21
Antigua, Guatemala
The interesting question I'm seeing hinted at is the one of on-demand heating. I was told that these heaters are on demand, and that you can essentially leave them turned on set to the desired temp, and that all one has to do to "turn on the heater" is to flip the circulation pump. As long as it's properly valved so that the water is properly circulating through the heater, the heater kicks on some kind of internal pump/flow, and about 10 seconds later the heater ignites. Is this not the proper way to do things?

It's easier for me to do it this way because I have guests and the more complicated things get and the more they have to flip switches the more can go wrong, but of course if one method is better than another for the system there's not question I need to do that.
 

ajw22

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Jul 21, 2013
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I guess I'm not seeing how that is very different from what I have, except that it eliminates the human error element that the three way switch solves. But as long as that all three valves are turned on that H, the result should be the same, no? Or is it affecting the flow or pressure in a way I'm not understanding?

Yes, a 3 way valve and a check valve on the heater output eliminates human error. Also the check valve will prevent water from backflowing into the output side and release any pressure in the heater should it turn on. Unlike the existing ball valve that totally locks the water and pressure within the heater.

I agree with the conclusion that the heater is likely turning on while both valves are shut and building pressure in the heater that cracks the manifold. The check valve would not let the pressure build like that.
 

alleycats

Member
Mar 16, 2021
21
Antigua, Guatemala
Who is to say that there isn't another valve somewhere closer to the spa and they adjust it for what they would call a comfortable flow at the same time you have this heater running with not enough water flow. The water is cooked and not enough to absorb the heat, kaboom.
We don't have any kind of valve to limit flow. The water from the outlet of the manifold is sent in a direct line into the jacuzzi (in the form of two jets installed on the sides of the "tub").

Here's a pic of the jacuzzi that I happen to have on my computer. I'm basically standing in front of where the heater is in the first pic and in the second you can see the machine room door and the heater is just above that (and kind of behind the tree and spiral staircase):
 

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alleycats

Member
Mar 16, 2021
21
Antigua, Guatemala
Yes, a 3 way valve and a check valve on the heater output eliminates human error. Also the check valve will prevent water from backflowing into the output side and release any pressure in the heater should it turn on. Unlike the existing ball valve that totally locks the water and pressure within the heater.

I agree with the conclusion that the heater is likely turning on while both valves are shut and building pressure in the heater that cracks the manifold. The check valve would not let the pressure build like that.
Is there any way that that could be happening on it's own? We have the machine room locked so no one can get in there, and I myself leave it set to flow through the heater before guests check in, and then I even kick it on briefly to make sure the heater fires up. I guess what I mean to say is that in theory the heater only turns on when water runs through it, and water only runs through it when I switch the valves so they run through heater instead of looping directly back into the jacuzzi (by passing heater to filter).
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
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Northern NJ
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The interesting question I'm seeing hinted at is the one of on-demand heating. I was told that these heaters are on demand, and that you can essentially leave them turned on set to the desired temp, and that all one has to do to "turn on the heater" is to flip the circulation pump. As long as it's properly valved so that the water is properly circulating through the heater, the heater kicks on some kind of internal pump/flow, and about 10 seconds later the heater ignites. Is this not the proper way to do things?

The heater can be left on demand as long as the pool circulation pump will always run before the heater will go on. There is no internal pump in the heater. The heater has a pressure switch and not a flow switch.

The pressure switch is supposed to indicate that there is water in the heater. The problem is with your two valves closed you lock pressure in the heater and the pressure switch tells the heater that there is water in the heater but does NOT tell the heater if the water is flowing.

Having water pressure in the heater but not the water flowing is the setup for your problem. That is why James says you need to have a flow switch.
 

alleycats

Member
Mar 16, 2021
21
Antigua, Guatemala
I agree with the conclusion that the heater is likely turning on while both valves are shut and building pressure in the heater that cracks the manifold. The check valve would not let the pressure build like that.
And by "check valve" do you mean the flow switch that others are recommending?
 

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