My client's heat exchanger got blowed up.

JohnNY

It even blew the bolt heads off. We found it like this during a recent heavy rain. The flue was full of water. The condensate neutralizer was draining too slowly. I think they should rewrite the manuals to show flue piping terminating with one two 90s. Many show a straight up, open termination.

pecmsg

Are you letting the factory know?

pecmsg

shouldn’t the pressure switches prevent it from firing?

JohnNY

pecmsg said:

Are you letting the factory know?

Yes I am. I let the rep know but he described what I was looking at as quickly as I was. Seems like a known failure to some degree.

pecmsg

JohnNY said:

Are you letting the factory know?

Yes I am. I let the rep know but he described what I was looking at as quickly as I was. Seems like a known failure to some degree.

That’s Scary!

mattmia2

https://slm-assets.secondlife.com/assets/5390820/lightbox/George-Takei-oh-my.jpg?1334189545

JohnNY

pecmsg said:

shouldn’t the pressure switches prevent it from firing?

Interesting. Yes they should. Maybe my failure theory is wrong. I connected the HX failure with the pooling in the flue, which, when looking at it and in the absence of any other leaks, seems like a solid assumption.

mattmia2

Maybe the moisture wasn't blocking flow completely but was causing delayed ignition.

HVACNUT

I wonder what the minimum RPM on the blower is to  allow trial for ignition.
MacGyver would put a float switch in the flue.

EBEBRATT-Ed

Delayed ignition would be my guess, blew the gasket out melted the pvc

kcopp

Makes me wonder if the burner mesh had a failure.

EBEBRATT-Ed

@kcopp. There is no mesh anymore LOL

Zman

Those triangle studs on top are famous for spontaneously snapping like that. It looks like you are missing 2 or 3. It probably ran a while like that, the burner doesn't know the difference as long as the flame is proving.

Solid_Fuel_Man

I'd think that a no flow situation with a negative pressure gas valve would not let any gas flow......

But a leak in that silicone gasket or elsewhere would allow gas flow and poof.

Another but....if the gas valve were leaking just a little and the blocked flue didnt flush the gas out on pre purge.....BANG!

The burned PVC pipe makes me thing some flue gas was leaking beforehand around the silicone gasket. It seems one sudden explosion wouldnt have enough heat for long enough to make it do that beyond just a discoloring in that spot. 

Tim_D

I suspect that this is the result of repeated delayed ignition issues or low fire issues. The only way to melt the silencer is through a backfire. If the combustion is not set properly the burner can overheat on low fire and the fuel air mix ignites inside of the burner instead of on its surface resulting in a violent explosion. I would think that a blocked flue would just shut it down.

Zman

The studs on that heat exchanger probably have a 5%-10% failure rate with no one touching them. It may have been a pre-ignition, or they may have just snapped off. This is not a one-off issue for that model.

JohnNY

All interesting theories. One delayed ignition may have caused the big pop but doesn't explain the burn on the PVC, which as suggested, I would think would take some time to make happen. Still, we found it in lockout so yeah, maybe the gasket/bolts failed earlier than the ignition failure.
Anyway, it's in the back of my pickup and I'd like my rep to take a look at it.
Good guys at Thermco in NY/NJ.

Colorado_Dave

I've seen 4 of the first series have the burner gasket fail like that.... just today had one that a previous tech walked out on after he replaced it and had high CO numbers (150+) ... but two of the posts in top are broken. 

JohnNY

Colorado_Dave said:

I've seen 4 of the first series have the burner gasket fail like that.... just today had one that a previous tech walked out on after he replaced it and had high CO numbers (150+) ... but two of the posts in top are broken. 

Wow. This is my first time encountering this. The boiler is 10 years old. Were yours about that age as well? I think the heat exchangers are a different design now but I'm more of a Weil-McLain/Lochinvar guy than TT.

Derheatmeister

IMO most likely a delayed ignition broke the bolts which melted the gasket then the exhaust gas melted the Tube...
There can be many reasons for a Delayed Ignition such as fouled or Mal adjusted rods.
Generally when we encounter this issue the heat exchanger was not maintained or cleaned/Traps are clogged/Rods are Fouled up..

RayWohlfarth

Yikes that's scary

HomerJSmith

Interesting!

Dennis Bellanti_2

The manufacturer of this heat exchanger used an incorrect alloy to weld the studs on to the heat exchanger. Over time the heat and cool cycles caused the weld to stress crack and eventually break. Typically most if not all studs will eventually break. They have since rectified the issue and TT covered the issue under warranty.

JohnNY

Dennis Bellanti_2 said:

The manufacturer of this heat exchanger used an incorrect alloy to weld the studs on to the heat exchanger. Over time the heat and cool cycles caused the weld to stress crack and eventually break. Typically most if not all studs will eventually break. They have since rectified the issue and TT covered the issue under warranty.

That's fantastic, Dennis. Thank you.

gennady

I think the boiler was working for a while with a compromised gasket and/or studs.


We caught a similar problem on 2 million BTHU boilers during maintenance, done for the first time in 10 years after installation. Lucky client, these heat exchanger covers were about to fall off.

Kal Row

i service a ton of modcons, all brands and sizes, happens a lot to these - but if you have proper venting, and do a full cleaning every year including neutralizer service it almost never happens - and this is a problem with all mod cons - some worse than others - and bad venting is the most common cause
when this happens the manufacturers try to get out of the warranty claim by stating that proper maintenance was not done - and my response is, that proper maintenance I.E.: cleaning,flushing, ignitor/flame rod replacement, neutralizer update, combustion analysis - runs 500$ per boiler per year, and if i told the customer up front that they have to spend 500 per boiler per year - you are not selling another boiler - so that argument is a zero sum game

manufactures also have to do install "pictorials" - when you open a computer box you get a picture fold out of how to set it up, boiler manufacturers need to do the same - as most installers dont read, even if they can - so you do it in pictures or dont do it at all - especially the VENTING!!! bad venting sinks modcons!!! i beg installers to do the venting first.

lots of people have taken to only installing wall-mounts under 2k in cost, so that when things get dicey they throw it away and pop on another one - of course you have to make sure that the first install was a DFD (Designed For Disassembly) install

compare the TOTAL cost and AGGRAVATION of 30years of radiant with modcons - vs - a single pipe steam system with a mechanical feeder and millivolt gas valve that doesn't even need the electric co, the comparison will make the modern technology look ludacris!!!

one combustion fan change and the value of 10 years gas savings is gone!!!

I AM GUILTY!!! i have designed GREEN systems!!! and caused lots and lots of suffering!!!
Efficiency? BAH-HUM-BUG!!!! , two "F"s in the word, never heard anyone pronounce the second "F", not very efficient is it?

tim smith

John, been there seen that, bolt broke off from thermal stress, flue gasses blew out right against the intake pipe, finally melted all the wires and shut down, kinda scary. John, the bolts on the old solo boilers had a weak weld, over period of several years they pop their friction weld, very minimal weld contact there. But what you will probably find is the tubes are restricted down inside where they are pinched in for heat transfer. We have found some with 80% blockage and real hard to get somewhat clean. May be due for new heat exchanger? Try sticking a silfos solder stick down the tubes, they are thin and stiff, we run them down on either side of dimples on each tube after soaking and washing.

tim smith

a side note, I have always thought these condensing boilers should have some sort of pressure proving on combustion chamber pressure. If too much back pressure they won't fire.

tim smith

We have never had any studs break on the smaller Triangles, the 175s and 399s have had many pop off. Just a little tidbit. More 399s although. Only on the older PS series boilers not the later PT and so on.

mattmia2

tim smith said:

a side note, I have always thought these condensing boilers should have some sort of pressure proving on combustion chamber pressure. If too much back pressure they won't fire.

It is more than that, it is like a supercharged and carbureted engine, you are pressurizing air fuel mixture so if there is a leak you are leaking the perfect mix to burn or explode. Not quite sure if there is a good way to detect that but the current designs don't even try.

Zman

Dennis Bellanti_2 said:

The manufacturer of this heat exchanger used an incorrect alloy to weld the studs on to the heat exchanger. Over time the heat and cool cycles caused the weld to stress crack and eventually break. Typically most if not all studs will eventually break. They have since rectified the issue and TT covered the issue under warranty.

This is the definitive answer. The rest of the conversation is just diluting the answer to the original question.