Cracked Heat Exchanger?

Slowhand63

I have a very long thread on here with all of the issues I’ve had over the last few months, but thought I’d repost with a more direct question for those not inclined to wade through 6 months of history.  

I have two American Standard 80% eff furnaces bolted together that run in tandem to heat a 5500 sq ft poorly insulated house (AUC1D120A9601AD).  

Yesterday morning I found one unit with no flame while the other was running.  The igniter cycled and the furnace lit - but the flame was dancing wildly then went out.  I did not check the error code on the control board before powering both units down. 

I removed a burner - photo attached - but don’t have the experience to know whether the burners could be the issue.  

From what I’m reading on the forum it sounds like it could be a cracked heat exchanger - ?  Anything else (preferably less expensive and replaceable) that it could be?

All comments/suggestions greatly appreciated.  

EdTheHeaterMan

One of the tests I used to test for a breach (or crack) in the heat exchanger is to observe the flame with the blower on and the blower off. If the opening is large enough there will be a difference in air pressure on the cell that has the crack when the blower is on compared to the blower off. That difference in the air pressure will affect the flame. This is further verified with combustion testing instruments. This may be a little more involved when a furnace is twinned since both blowers operate in tandem. You will need to power off the furnace that you are not testing. Then operate the burners only on the problem furnace, and observe the flame. While the flame is operating, turn on the fan for that furnace and watch the flame on the suspect burner. If there is a substantial change compared to the other burners, you have a crack.

Slowhand63

Ed

Thanks for your response. I’ve watched a couple of YouTube videos about performing a static pressure test - but I have a few issues:
 - the suspect furnace is “#2” and power is supplied from #1.  I could probably run a 110v line directly to #2 but will take a little work.  

 - I have no idea how to get the furnace to burn without the blower kicking on, and how to then initiate the blower
 - I accidentally broke the igniter. New one on order will arrive tomorrow.  

I appreciate the suggestions on how to confirm if I have a HEX issue. 

More importantly - could the symptoms I describe be caused by anything else?

Thanks - Bill

mattmia2

Slowhand63 said:

I have no idea how to get the furnace to burn without the blower kicking on, and how to then initiate the blower

Not sure what to do about the twinning, but basically just jumper r and w and turn the power on to make a call for heat and either jumper r-g after the burner lights or wait for the fan control or time to turn the blower on while you watch. Having a co detector around while you do it is a great idea since you don't want to give anyone co poisoning while you're testing. A couple minutes testing won't do that if it is burning somewhat properly but if it is burning very poorly it could be dangerous.

Slowhand63

Mattmia2 

Thanks for your response.  Without the replacement igniter I’m dead in the water until tomorrow.  

Thanks for the insight on how to jump the controls.  Very helpful.  What you describe below sounds no different from the heating cycle, correct?  If I punch up the thermostat a couple of degrees the furnace will light and burn for a predetermined time (30 or 45 sec I think) then the blower kicks on.  MYbe I’m missing something?

The static pressure check I’ve seen is to run the blower ONLY without the furnace burning, and placing a long-stick match into the the burner ports to see how the flame reacts.  No change = no leak. Change in flame = leak.  Does that sound right?  And if yes, can I get the blower to run (with thermostat in OFF position) by jumping  r+g?  Obviously I need to make sure the gas valve doesn’t open or I’m toast.  

Also - still looking for other potential causes for a dancing flame other than a cracked HeX.  Maladjusted gas valve?  Clogged orifice?  Bad burner(s), … ?

Thanks in advance,
Bill

mattmia2

You can do it with the thermostat too but it is a little more difficult to make sure you're there when the blower kicks on.

Jumping r-g will turn then lower on. turn off the manual gas valve if you're going to stick your hand in there.

Other cause would be the pressure isn't stable because of something wrong with the regulator in the gas valve or possibly the meter, checking that would involve hooking up a manometer to the burner manifold. If the passages in the hx or the vent are clogged it could cause something like that too.

dullknife1

How old are your heaters?

One of the easiest tests is to grab a box of fireplace matches. Turn the gas off , with blowers off,run a lit up match as far in and out of every burner chamber starting with unit number one because that has the least amount of fluctuation if none. There should be a little to no fluctuation in the match unless it’s a severely windy day blowing down the chimney.    Turn the blowers on and repeat test,(still with gas off,) and running lit  matches up and down the heat exchangers over the burners. when you get to the burners that blow the match out, you have found the culprit. depending on which burner it is there a few things you could do as a temporary repair, but I will not discuss that here especially going into the summer season. Chances are if your American Standard is over 25 years old, you have a crackhead exchanger, you probably have a big old hole in it can’t see. Sometimes the old saying” I think I can get one more year out of it just doesn’t apply“.

Larry Weingarten

"crackhead exchanger" ?? Better watch out! You're in @EdTheHeaterMan 's territory here I do like the fireplace match idea

Yours, Larry

dullknife1

Sorry Larry, but judging by the photo of the burner, it looks like it comes off a very old heater. And I have a hard time working through this formum. took me 20 minutes to get back to to mention this   if the first heaters working, OK, and the second heater sounds like it probably has a problem, no sense taking chances, disconnect the gas from the second heater. Run the first heater as normal. A little heat is better than no heat. I don’t know where this heater is or how cold it is. I don’t know what kind of fan switch it has in the second heater (timed or temp controlled). If Blower is not coming on (because it’s a temperature controlled fan control )put  2nd heater thermostat on the fan on, just to move some heat that section. 

dullknife1

LOL. Just saw the crackhead, heat exchanger spellcheck,  I meant correct, heat exchanger

Slowhand63

The two twinned units were installed about 12 years ago (I can check pwk later to confirm - it’s in a binder next to the furnace).  

Just to confirm the process…. To perform the fireplace match check I remove the burners and place the match into the chamber, correct?  Main gas line closed (2 consecutive valves for safety), manual switch on gas valves set to off, remove burners, place lit fireplace match into each chamber where the burner(s) enter.  Then repeat with the blower on (blower is turned on by jumping a wire on the control board from r to g).  

Correct?

Although I’d be interested to learn about a potential repair, I don’t think I’d be comfortable doing that myself.  Either it can be done by a pro, or I’m going to need to invest in a new unit. Unfortunately that means two units - doubling the cost and doubling the fun!

For anyone interested, I am on Long Island in NY - mid 40’s at night.  

I ordered a complete set of burners, orifices, two ignitors and two flame sensors ($300+).  From the comments here - other than replacing the broken igniter - it sounds like none of that is going to help me - correct?

EdTheHeaterMan

Parts Cannon Apprentice. You might want to get some new gas valves and a couple of fan timer boards. combustion fans are also expensive too. maybe even a new blower motor. After all those parts are in your posession, you might take the heat exchanger out and look at it. Then you can order the new heat exchanger after you actually see the crack.

I might choose a different order of diagnosing this problem. I remember that you took some parts from one furnace and moved them to the other furnace and the problem moved with the parts. I don't think that the bad heat exchanger cell would leave me to suspect a cracked heat exchanger.

I wonder if there is a fairly good HVAC contractor that has a decent trouble shooter located near you. Sometimes it is just time to break down and admit your limitations.

mattmia2

I have no doubt that someone here knows someone in long island that knows forced air.

yellowdog

do a combustion efficiency on it. if the numbers jump around when the blower comes on, you have a crack.

dullknife1

Yes that should show flame fluctuation between the two tests, if you have a cracked heat exchanger. A quick pause here for 2023 definitions. With the new cheaply made thin metal pressed heat exchangers, we don’t call them cracked heat exchangers anymore. We call them heat exchangers with air leakage. Because now some of them come with seals and the seals link so that exchanges are not actually cracked but there’s still leaking air.  So you don’t have to have a cracked heat exchanger to  have an air leakage problem. So enough of that !If you have an inducer motor on this unit you need to pull the molex apart so no inducer is not on either test. but I will leave you with this. There are three steps to making carbon monoxide and killing people. Step number one a blocked chimney step number two a cracked heat exchanger or an exchanger that’s leaking or cracked. Step number three the big one, the air that could not escape the chimney like it supposed to that has already been through the flame combustion process rolls back into the heater room and goes through the combustion process again. Once that compromised air is burned twice that’s where you get carbon monoxide and if you have a cracked heat exchanger or exchanger that is leaking, that is the air that gets pushed through the forced warm air ducks ,so at a minimum whoever and wherever you are make sure your chimneys are clear before every heating season and possibly check them twice a year. I. This can happen with any heater with it without the dampers with or without chimney caps. You always have to be safe. I saw a squirrel chew true through a stainless steel chimney cap build a house halfway into the chimney liner and the chimney itself. Now the shaft this chimney was less than a month old and I had to condemn the chimney. The homeowner was furious, but I couldn’t get a mirror up there because of the bend of the the chimney. So I couldn’t prove it,visually. I happen to be driving down the street a couple days later, and the 
The customer was out there, talking to his neighbor ,I had to stop. Customer shook his head and said I was right as we stood there and watched this pregnant squirrel scream bloody murder from the top of his roof even though it was 35-40s yards  away the hair on my arms stuck straight up. 

dullknife1

Hopefully last comment, if you’re not comfortable with jumping r and g ,set both thermostats on fan on only no heat no cool just fan on and work the fan by the power switch on side of heater. But here’s another caution, if you jump r+g electricity doesn’t know color I’ve seen regular forced , warm air units wired with three sets of two wire, red and white. Be careful. see you in them wired with five of the same color. 

Slowhand63

dullknife - thanks for the word of caution.  I’ve been around the control board many times - I’m pretty certain the wiring follows normal convention - but I will double check to be sure.  

Also - thanks for the commentary on CO.  I have a CO monitor/alarm mounted on the ceiling joist just above the units.  Both units are vented through (5”?) PVC that runs at a slight pitch upward and out the side of the house.  As they exit the house there is a 90 and they point down.  There’s a grate in each one to prevent animals - and I’ve checked them and they appear clear.  

Still waiting on the arrival of the replacement igniter.  After install I will fire the unit up and see how it does.  I’ll take a short video if the flame is dancing.  

If and only if the flame is unsteady will I go back in and test for air flow issues with the HeX.  Based on what I find I may be looking for a good service tech.  If anyone knows anyone - please recommend.  I am in western Suffolk county (Babylon).  

Lastly - I’ve chosen to ignore Ed’s last post.  I guess he was having a bad day yesterday.  

JUGHNE

You mentioned 80% furnaces but then just commented PVC exhaust pipe out the side wall.

Hopefully you have 90%+ condensing furnaces.

Pictures from a distance back, with doors removed, would be good.

mattmia2

What parts did you swap? a bad hx wouldn't follow parts swaps.

there are 3 common possibilities, one of the orifices is clogged, the regulator in the gas valve is bad and the furthest burner isn't getting enough gas to even burn smoothly, a burner is physically damaged or clogged(this would be pretty obvious if you compared it to the other burners.)

If you swapped power vent parts there could be some things with that.

Slowhand63

Ed - it’s quite possible that there’s a good troubleshooter close by - but I’ve also run across my share of incompetent techs. I could name them - the first being the system installer - but I’d consider that rude.  Swapping parts - especially from one working unit to another - is a pretty common approach, especially when done following a logical sequence based on knowledge of the system, which is what I’ve tried to do.  Yes, I’ve made some mistakes - and asked some stupid questions - but I’m learning as I go.  I do have to put up with occasional snarky comments - but that’s life.  

I’ve probably dropped $500 on the furnace in the last 6 months.  I think that’s probably 3-5% of what replacing the units would cost, and maybe a couple of hours of a tech’s time.  Over the last few years I’ve probably saved myself 10x that troubleshooting issues on my own and with the help of those on this forum. 

I greatly appreciate your help - and the help of others, but I can do without the snark. 

Slowhand63

The parts I ordered arrived late yesterday.  I installed the new igniter and everything seems to be running fine. 

mattmia2 - the parts swap comment is related to an issue that started 3-4 months ago.  I posted about it and have a long thread on here. On some mornings during the long heating cycle (to bring the house up to temp after the lower thermostat set point overnight) furnace #2 wouldn’t be running and I’d have a 3-flash error on the control board.  Since the units are identical - I first swapped the pressure switches, and then the inducer.  I also put everything back to its original place and installed a new P switch and inducer.  Nothing solved the problem.  The problem was always intermittent - happening every couple of days - and then stopped occurring.  

I’ll take some photos of the setup and post later today.  

The parts I ordered are returnable.  I broke the igniter and ordered two - one installed and one will be a spare.  I ordered two flame sensors - the ones installed are the originals. I may pull the one on furnace #2 and replace it (though I’m hesitant to change too many things at once). I may return the burners, although there’s some surface rust on the ones in use I don’t see anything that I’d consider a clog.  The orifices are pretty rusty - I might choose to change them out.  For $80 or so it’s money we’ll spent.  

If I change the orifices - do I put anything on the threads or do I simply screw then back in?

Thanks to all for your comments/help/suggestions.  It is very much appreciated.  

dullknife1

JUGHNE
Is right.  What heater are you trying to fix.  80% troubleshooting is a little bit different than 90% troubleshooting. I will repeat what has been said , take a picture of the unit, if 90* good picture of condensate collector plate

dullknife1

If you have pvc for in and out gas you have to make sure no obstructions. I worked on the heater one year where the flames went to the dance after about 15 minutes of running. Consistently.  It was only a couple years old so I could not go to the air leakage theory. Long story short there was a mud wasp house built in the exhaust part of the pipe, which was not easy to get to. So when the heater didn’t run and it dried out, it was fine as soon as that mud got wet enough to obstruct the air flow, the flame started doing the twist. I cut out the mud house put in a Fernco, and everybody was happy,except the wasps.

dullknife1

The model number given for your heaters is an 80% heater. You might want to i’ve never seen PVC used on an atmospheric 80% heater. Look around for your instruction manual.

dullknife1

I meant installation manual they should be together

Slowhand63

Furnace ran fine this morning.  It’s 70 deg here on LI and we are outside - so the heat is OFF.  

Photo taken as requested.  

Units are 90% eff (92% to be more exact, I believe).  

Thanks to all following and commenting on this thread.  

Slowhand63

Also - I looked up the 90’s outside the house.  Not much to see but no evidence of anything inside the pipes.  There’s a good run of pipe - probably 20-25’, and no way to inspect it without a boroscope or cutting the pipe out and replacing it.  

Slowhand63

I just noticed my photo didn’t do a good job capturing the gas supply. The line runs overhead from the RHS of the photo (above furnace #2) and there’s a tee above so that F2 is fed.  The line continues and then comes down the LHS of F1 and to the gas valve.  

109A_5

Slimpickins

I would make sure the exhaust vent pipe is pitched back to the furnace with no sags. Also check your venting tables in the manual, if I remember correctly on the 120K BTU it's 60'. Also, it would be a good idea to check gas pressure.

dullknife1

Two units running at the same time produce a lot of condensation, are all your condensate lines, clean, clear, including wherever it goes after the PVC pipe. You have two pressure switches coming off of the valve down by the bottom of the collector plate. They can play havoc when you’re not watching. and you have a sealed combustion process unit air coming from the outside going through the burner process going to the outside any fluctuations and that airflow will fluctuate the flames on the burners. It could be as simple as your condensation not running smoothly. Hopefully that’s all it is unless of course you’re already checked. that

dullknife1

On that note, the little metal pipe comming off (out of) the condensate plate, the one that ties into the  pressure switch with tubing,that goes in the valve . Feel free to stick a paper clip in there and clean up all the crap that’s been building up behind that little port for however long they have been running. 

Slowhand63

Condensate lines are clear.  The small pvc line runs straight down into a condensate pump which cycles every time the furnace cycles.  I’ve removed the small tubing lines - they are clear - as well as removing and flushing the condensate collection box a few months ago.  

Since the problem is intermittent - happening infrequently - I’m wondering if it’s a gas pressure problem (though there are no gas-powered appliances running on the first heating cycle of the morning when the issue occurs). When the units were orig installed gas pressure was a concern so the meter was replaced (upsized).  

It’s warming up here in NY and the units are on the verge of being shut down for the season.  I think my next step is to get a good tech with the proper tools to measure exactly what’s going on with the system.  

dullknife1

Is your gas system a UP system or pressure system?

dullknife1

Jump the t-stat.   Now is when you want an answer, not when it’s 10*

Slowhand63

I’ve been told it’s a low pressure system, but don’t know much more about it.  I get the point about getting it fixed now - and not waiting until next winter - but I need to find a good tech first.  

Does anyone have a recommendation of someone serving Suffolk County, Long Island NY?

dullknife1

Please take a picture of your gas meter. From ground to the take off pipe 

dullknife1

Did you read “the case of the rainy day boiler” by Ray Wohlfarth on May 6th?  A picture of your whole meter world still answer most pressure or no pressure problems

Slowhand63

Okay - here are some photos.  Apologies for the meter photo - if the Ivy is in the way let me know and I will attempt to clear some and take new photos tomorrow.  

Once the line enters the house you can see the orig (painted gray) gas line and the larger diameter line that feeds the boiler.  When the meter was replaced I was away in Denmark and when I returned I wasn’t happy with the install - you can see a small diameter (1/2” or 3/4”) nipple supplying the larger supply line to the furnaces. 

I took a photo of the furnace feed line as well.  

Let me know if these are sufficient or if I should take any additional views.  

Slowhand63

dullknife1

That’s a pressure gas system. Probably 15-60# of gas under that regulator. Chance of pressure problem small but if your gas company will check for free that’s the way to go. Ask to check with a u-gauge on 2 nd heater drip leg. First with nothing running,2nd with everything running   First check called lock up pressure shows that you have gas, but 2nd check shows if the regulator ( outside before your meter) is working or not.  This will only answer if you have a gas pressure problem on the gas service. Unfortunately this will not tell you if the is a problem across the gas valve at the 2nd heater. If the gas company will do the service test ask if he, or she would like a cup of coffee and ask if he can put that u/gauge on the outlet port of the valve in question.