Persistent Failed Ignitions on a Triangle Tube PT-250

Avery1980

Hi folks,

We recently purchased a home with a Triangle Tube PT-250 mod con running radiant heat and hot water. For full disclosure: we're novices at HVAC and trying to educate ourselves as we go.

The prior owners had the unit professionally installed in 2013 and were, as best we can tell, good about scheduling regular maintenance with the same company that installed it. They had ignition failures in 2021 and did the ignition kit update, which mostly (but not entirely) solved the problem.

We bought the home in 2022 and, unfortunately, the ignition failures have gotten much worse. We now see several lockouts per day. A manual reset is typically sufficient to get the boiler running again normally.

Techs have tried everything Triangle Tube suggested, including checking the gas pressure, checking the combustion, replacing the ignitor and gasket, replacing the venturi (which had deteriorated), replacing the combustion chamber insulation (which had also deteriorated), and doing a thorough cleanout of the combustion chamber and burner (which had coffee grounds gunk). Everything looks right when the burner fires, and the boiler works normally for awhile (cycling on and off with CH and DHW calls and modulating to hit the target temperature). Then, eventually, there's a sequence of five failed ignitions and the unit locks out.

We'd greatly appreciate any pointers on other steps we might take to identify and correct what's causing the ignition failures. We're already into this thing for thousands of dollars, since Triangle Tube refused warranty coverage because we aren't the original owners (even though these issues kept coming up for the original owners and we raised them within the 10-year period). We really don't want to replace the boiler when it's barely 10 years old, runs just fine otherwise, and still has good parts availability.

Thanks for any pointers you might be able to offer!

GGross

"replacing the venturi (which had deteriorated)" The only thing that destroys the venturi is flue gas cross contamination to the intake. Your boiler is sucking the flue gas back in and trying to fire with the flue gasses. It must have been doing this since install and that can cause numerous other semi hidden problems down the road. After replacing the venturi did your service tech use a combustion analyzer to properly set combustion? If they have been doing things correctly they should have left all of the combustion analyzer print outs. Did you notice them using a digital analyzer with a probe inserted into the flue pipe at any point?

I would say that if a tech saw the venturi destroyed and didn't immediately move the intake pipe that you need to hire a different company. Someone absolutely must set up the combustion on this unit with a digital analyzer, and whoever comes to do that needs to make sure the ignition update was performed correctly. No analyzer means it has not been done correctly

tim smith

Re: most condensing firetube boilers, agree on the flue gas recirc on venturi. Other thing that many overlook is the coffee grounds in combustion chamber get vacuumed out and usually chamber cleaned but the 20 - 40 tubes (depending on size) that run down through the heat exchanger to the condensate pan become blocked with the grounds. They do not come out with rinsing out, putting cleaner down. They are stuck in the small tubes at the dimple locations of each tube. There are dimples in the very narrow tubes all the way down. The grounds start to stack up in the tube over period of time. They are hard to get out.
See photo of cutaway of heat x and depiction of what we find is in orange, can be
anywhere up and down tube. They also become very hard over years from combustion firing over them down through the tube and make it even harder to clear. We have had to use flat stick brazing rods to clear as best we can when they have gone too long between cleaning. This procedure in not in maintenance procedure manual, we just found there was no other way to clear to reduce backpressure in heat x during firing. The crystals get really hard and we have not found a safe chemical to break them down.

Avery1980

GGross said:

"replacing the venturi (which had deteriorated)" The only thing that destroys the venturi is flue gas cross contamination to the intake. Your boiler is sucking the flue gas back in and trying to fire with the flue gasses. It must have been doing this since install and that can cause numerous other semi hidden problems down the road. After replacing the venturi did your service tech use a combustion analyzer to properly set combustion? If they have been doing things correctly they should have left all of the combustion analyzer print outs. Did you notice them using a digital analyzer with a probe inserted into the flue pipe at any point?

I would say that if a tech saw the venturi destroyed and didn't immediately move the intake pipe that you need to hire a different company. Someone absolutely must set up the combustion on this unit with a digital analyzer, and whoever comes to do that needs to make sure the ignition update was performed correctly. No analyzer means it has not been done correctly

Thanks to you both for flagging the possibility of a flue gas venting problem.

The boiler is installed with a concentric vent through a nearby exterior wall. I believe the vent was made by Triangle Tube and approved for use on this model.

The most recent tech used a digital combustion analyzer and provided a printout. He noted that the unit was miscalibrated with too much gas supply, and he adjusted the gas valve offset and throttle. Here's what the analyzer printout said:

Fuel - Natural Gas
CO2max - 11.8%
7.4% - O2
24ppm - CO
76.1C - Fluegas Temp
85.2% - EFF
--.-ppm - Ambient CO
20.2C - Ambient Temp
--.-inH2O - Draft
171.4% - Excess air
--.-inH20 - Pressure
4.35% - CO2
68ppm - Undiluted CO

The post-adjustment values were close to but not within spec, which the tech also noted. Interestingly, both the CO2 and O2 were high. He offered to come back to dial in combustion when, at Triangle Tube's recommendation, the system had cooled down. He thought it was very unlikely that the deviation from spec was causing the ignition failures, though.

I'm not sure what to make of this, and I really appreciate the expert perspective.

Avery1980

tim smith said:

Re: most condensing firetube boilers, agree on the flue gas recirc on venturi. Other thing that many overlook is the coffee grounds in combustion chamber get vacuumed out and usually chamber cleaned but the 20 - 40 tubes (depending on size) that run down through the heat exchanger to the condensate pan become blocked with the grounds. They do not come out with rinsing out, putting cleaner down. They are stuck in the small tubes at the dimple locations of each tube. There are dimples in the very narrow tubes all the way down. The grounds start to stack up in the tube over period of time. They are hard to get out.
See photo of cutaway of heat x and depiction of what we find is in orange, can be
anywhere up and down tube. They also become very hard over years from combustion firing over them down through the tube and make it even harder to clear. We have had to use flat stick brazing rods to clear as best we can when they have gone too long between cleaning. This procedure in not in maintenance procedure manual, we just found there was no other way to clear to reduce backpressure in heat x during firing. The crystals get really hard and we have not found a safe chemical to break them down.

Thanks so much for flagging this, too. I'm unsure if the tech inspected these tubes, and I don't believe he tried poking them with anything to clear them. Could a blockage like that cause ignition failures?

tim smith

absolutely can cause ignition failure. You can't see down the tubes, also with the later pt boilers they have offset the dimples making it impossible to get down the tubes with a rod. This is not a recommended procedure by manufacturers but only way we have been able to clear. The older models than you have had a dimple pattern right down the middle of tube which allowed us to go down each tube on either side of dimple and clear, mostly. The new offset dimples keep us from getting down tube.

Alan (California Radiant) Forbes

Did the tech pour any water down through the top of the HX. Some use a strong spray to get out all the debris.

How is the condensate trap connected to the drain at the bottom of the HX? Is it directly connected or is there an air gap? Do you have a condensate neutralizer?

Avery1980

tim smith said:

absolutely can cause ignition failure. You can't see down the tubes, also with the later pt boilers they have offset the dimples making it impossible to get down the tubes with a rod. This is not a recommended procedure by manufacturers but only way we have been able to clear. The older models than you have had a dimple pattern right down the middle of tube which allowed us to go down each tube on either side of dimple and clear, mostly. The new offset dimples keep us from getting down tube.

This is really helpful. In your opinion, would it be worth trying this outside-the-manual cleaning procedure before just throwing in the towel? I suspect that it would be in the range of a thousand, if the tech is willing to do it at all.

Avery1980

Alan (California Radiant) Forbes said:

Did the tech pour any water down through the top of the HX. Some use a strong spray to get out all the debris.

How is the condensate trap connected to the drain at the bottom of the HX? Is it directly connected or is there an air gap? Do you have a condensate neutralizer?

The tech used a vacuum, some boiler cleaning fluid, and lots of water. He had a spray device of some sort. As best I could tell, he did a very thorough job.

The condensate trap, which was replaced in 2021, is shoved onto a plug at the bottom of the boiler. There isn't an air gap, and there isn't any neutralizer in it.

EBEBRATT-Ed

4.35% Co2 cannot be right.

I would suspect flue gas recirculation as others have mentioned. Just because Triangle Tube supplied the concentric vent does not absolve that issue. No one can predict the wind currents at the vent location. Manufacturers and the equipment they sell are far from perfect.

I have seen plenty of jobs installed by the "book' that don't run well.

tim smith

Alan, pouring, spraying water pouring condensing boiler cleaners still does not get out the coffee grounds that become lodged in the tubes. It's a real pain. I have found them up to 70% blocked, overheating combustion chamber. Even with earlier models where flat silvfos rod could be shoved down the tubes on either side of dimples I found still left them + or - 20% blocked. Spent up to few hours trying to clear. Tough.

GGross

I would fix the venting first personally because we know that is absolutely not correct. Should you need to replace the boiler at some point the same thing will happen if you keep that vent in place. as Ed said flue recirculation can happen even on "by the book" installs, the recirculation issue is more of a field verified thing and even really good installers can't always predict how the winds will blow.

Avery1980

Thanks so much for all the expert perspectives here. I really, really appreciate it.

If we were to try to tackle the venting, what steps would you recommend?

GGross

Here is the install manual, they cover some general guidelines on combustion air starting on Page 5
https://cdn.triangletube.com/wp-content/uploads/2021/08/13135806/2011-50-Prestige-Solo-60-175-250-399-Installation-and-Maintenance-Manual.pdf

In an ideal world you would have the flue pipe vented vertically out the roof, and the combustion air piped out a wall, somewhere that didn't have other vents or the possibility of other contaminants. I always push for vertical flues if possible, but understandably it is not always possible


The basic idea here is to separate the intake from the exhaust, so that the exhaust gasses don't get pulled back in. You may be able to actually see this happening in real time if you run the boiler and go investigate the venting. Who knows maybe someone attached the vents backwards, it is always worth investigating that one in my opinion, usually just takes a few minutes to see how bad the recirc is. I have several times been called to check on boilers I suspected were recirculating and the installers had the flue piped to the intake on one of those concentrics, its pretty uncommon but I have seen it several times in the wild

Avery1980

Thanks so much. I've closely looked at the concentric vent install and the supplemental Triangle Tube guidance about it [1]. The boiler intake and exhaust are connected correctly and within spec. The only aspect of the install that's out of spec is that the vent extends out a couple feet from the exterior wall, when the maximum exterior clearance is supposed to be 1". Triangle Tube warns that this extended length "could cause condensate to freeze and block the vent pipe."

We're stuck with a horizontal vent, unfortunately. Would switching to a within-spec concentric vent install be the next thing to try? Or maybe a more conventional pair of intake and exhaust vents, snorkeled for separation? After correcting the venting, how could we tell that we've solved the exhaust recirculation issue, since the primary evidence is long-term degradation of the venturi?

Thanks again for all your help, everyone.

[1] https://hvacdirect.com/hvac/pdf/Triangle-Tube-PVC-Concentric-Termination-Supplement.pdf

GGross

If anything it sounds like they tried to separate the flue pipe from where the intake is by extending out the vent, I would honestly say if the pipe hasn't froze before that part is fine. You didn't happen to see the flue gasses exhausting out and back into the intake by chance? Could just be that it happens rarely with certain wind conditions.

Avery1980

It looks like the flue gas jets outward, away from the end cap of the concentric vent, with decent pressure. A mild breeze is enough to push the exhaust around some, including back toward the vent to an extent, though not much. Interestingly, there isn't noticeable intake flow around the end cap on the vent. I don't know if that's normal.

Here's a short video, in case that's helpful: https://drive.google.com/file/d/1GHyPy8W7fJWX1onx6zjZuRBM0OXijAde/view

Thank you again!

Avery1980

In case it might be helpful for diagnosis, I also made a short recording of the sight glass during the repeated ignition failures. (I kept my phone away from the internals and used the zoom.) The boiler does ignite on each attempt, starting with a blue-ish flame that transitions to an orange-yellow-ish flame, then it shuts off.

https://drive.google.com/file/d/1VTeZ1fsM6Ixm11M_xk8GNgDUhn8nXxfo/view

Happy Thanksgiving to all, and thank you again for all this expert guidance.

JMWHVAC

We had a PT60 on one job that kept doing ignition failures. I would go to job and the boiler would operate perfectly. Finally caught it in the act, the gas valve did not open. So replaced gas valve. Next day customer had to reset it again. Called factory, they said, "oh if gas valve didn't open and replacing it did not fix it, then it is the rectification plug for the gas valve". And that plug FINALLY ended the nightmare.

Avery1980

JMWHVAC said:

We had a PT60 on one job that kept doing ignition failures. I would go to job and the boiler would operate perfectly. Finally caught it in the act, the gas valve did not open. So replaced gas valve. Next day customer had to reset it again. Called factory, they said, "oh if gas valve didn't open and replacing it did not fix it, then it is the rectification plug for the gas valve". And that plug FINALLY ended the nightmare.

Thanks for flagging this possibility! How did you diagnose that the problem was with the gas valve? During the ignition failures, we're seeing a flame through the sight glass (video above) and gas flow at the meter. That suggests some gas is getting into the combustion chamber.

Alan (California Radiant) Forbes

Thanks for flagging this possibility! How did you diagnose that the problem was with the gas valve? During the ignition failures, we're seeing a flame through the sight glass (video above) and gas flow at the meter. That suggests some gas is getting into the combustion chamber.

I think what @JMWHVAC is saying is that it's not the gas valve that's the problem, rather the proof of a flame, called rectification.

The flame generates micro amps and if it's below a certain amount, it will shut off the gas.

kcopp

As to the venting that is not appropriate. That is way too far off the house. The vanes on the intake are supposed to be w/ in 1" off the house.
Furthermore how far from the corner is the vent? that will create an eddy for the wind to swirl around an suck in exhauset.
Typically the issue is not on high fire but of low fire where the exhaust does not get pushed out as far.
I am not a fan of a single pipe set ups. I only do 2 pipe. Much less chance for an issue.

This may not be the issue but long term it will help.

JMWHVAC

How I knew gas valve didn't open? No fire and the distinctive, soft thunk of the valve opening was not heard. The rectification plug (looks like its called rectifier cable on supplyhouse) is the actual power plug to the valve. It is a big plug as it has some rectifying electronic components in it. Could it be the plug on your boiler even tho its obviously lighting? I don't know but anything can happen with electronics?

JMWHVAC

When your boiler is doing the fire-up/ fire-out thing seen on the video, does the control see the flame?

CBRob

It might be time to just replace the boiler if you are spending thousands on trouble shooting.
A new triangle tube 199k instinct solo is under $3000.00 and install might not be too involved with swapping out another triangle tube boiler.
Ask your HVAC guy about it.

Avery1980

Thanks for all the invaluable expertise, everyone. I've bunched responses into this one post.

Alan (California Radiant) Forbes said:

Thanks for flagging this possibility! How did you diagnose that the problem was with the gas valve? During the ignition failures, we're seeing a flame through the sight glass (video above) and gas flow at the meter. That suggests some gas is getting into the combustion chamber.

I think what @JMWHVAC is saying is that it's not the gas valve that's the problem, rather the proof of a flame, called rectification.

The flame generates micro amps and if it's below a certain amount, it will shut off the gas.

Ah, got it!

kcopp said:

As to the venting that is not appropriate. That is way too far off the house. The vanes on the intake are supposed to be w/ in 1" off the house.
Furthermore how far from the corner is the vent? that will create an eddy for the wind to swirl around an suck in exhauset.
Typically the issue is not on high fire but of low fire where the exhaust does not get pushed out as far.
I am not a fan of a single pipe set ups. I only do 2 pipe. Much less chance for an issue.

This may not be the issue but long term it will help.

This is very helpful to know. The corner is a few feet away, so I certainly see how flue gas could build up and swirl back to the intake from there. I'll look into replacing our concentric vent setup with a two-vent setup, with the exhaust further from that corner.

JMWHVAC said:

How I knew gas valve didn't open? No fire and the distinctive, soft thunk of the valve opening was not heard. The rectification plug (looks like its called rectifier cable on supplyhouse) is the actual power plug to the valve. It is a big plug as it has some rectifying electronic components in it. Could it be the plug on your boiler even tho its obviously lighting? I don't know but anything can happen with electronics?

JMWHVAC said:

When your boiler is doing the fire-up/ fire-out thing seen on the video, does the control see the flame?

When the boiler fails to ignite, I hear the thunk of the gas valve, see a flame through the sight glass (like in the recording above), and see gas moving at the meter. I don't see a flame indicator on the boiler, however. Rectification could certainly be the problem. I've gone ahead and ordered a replacement rectifier plug, since it's so (relatively) inexpensive and easy to swap out.

CBRob said:

It might be time to just replace the boiler if you are spending thousands on trouble shooting.
A new triangle tube 199k instinct solo is under $3000.00 and install might not be too involved with swapping out another triangle tube boiler.
Ask your HVAC guy about it.

If the rectifier plug swap doesn't work, a new boiler is where we're leaning. While there are more things we might try, such as replacing the gas valve or the heat exchanger, those would be expensive guesses. I've been trying to educate myself by reading through the countless helpful threads on here about the tradeoffs of different boiler vendors and models, and how the expertise of the installer is at least as important as the unit.

Avery1980

Success! I was able to get the boiler working reliably again. Thanks to everyone here who shared their expertise. You helped solve a major problem for us and helped save us a massive amount of money.

Short version: If you're seeing ignition failures on a newish Triangle Tube model, and it looks like the cause might be unreliable flame detection, try reconnecting all the spark generator wiring per the directions or replacing the spark generator and all its wiring.

Long version: The symptoms indicated a flame detection problem, as suggested by folks here. The ignition cycle consistently looked right, with the blower coming on, the gas valve opening, the ignitor sparking, and a flame establishing. Sometimes the boiler display would then show a flame icon and the boiler would run normally. But sometimes, unpredictably (from minutes to days), there would be a series of ignition failures where no flame icon appeared on the boiler display, the flame would go out, and then there'd be a lockout. I tried to rule out other causes of ignition failure by working through all the diagnostics and recommendations I could find from Triangle Tube and online discussions: I had the degraded venturi replaced, had the heat exchanger thoroughly cleaned, checked that the incoming gas pressure and gas pressure drop were within spec, dialed in the combustion, and confirmed that the condensation trap was clear. That left the flame rectification circuit as a possible culprit.

I couldn't find any Triangle Tube documentation for how the rectification circuit works on these boilers, and there is no rectification-specific replacement part (unlike the rectification plug for older Prestige boilers). So I traced out how it had to work based on the wiring in the boiler and discussions on this forum about similar designs: rectification runs from the control board, to the spark generator, to the ignitor, to the rectification probe on the same component as the ignitor, then back to the control board. That narrowed down the problem.

I then compared the rectification wiring in our boiler to the wiring specified in Triangle Tube's ignition update kit directions and found, aha!, the tech who installed the kit for the prior owners a couple years ago hadn't properly connected either of the grounds. One goes onto a tab on the rectification probe wire and one goes onto the left side of the case. I connected those two grounds correctly and... still had the same ignition failure problem.

Since I had already replaced the ignitor (with rectification probe) on our boiler, I knew that was unlikely to be the culprit. That left the spark generator, all the wiring for the spark generator, and the control board. I had all those parts already, because they came in the ignition update kit I had ordered to get the replacement ignitor. So I went ahead with replacing the spark generator and all its wiring, following the directions in the ignition update kit... and the boiler started right back up! It's been running normally ever since.

Thanks again, everyone.