# Lennox Whisper Heat - Thermocouple/Thermopile issue



## tycho1974 (Oct 26, 2016)

Hello, everyone! I've got an issue with my small Lennox Whisper Heat gas furnace. After some troubleshooting, I think I've narrowed down the failure point to either the thermocouple or thermopile in the unit.










Typically, here's what's supposed to happen in my system:


Damper door opens
Pilot light clicks on (30 seconds)
Blower turns on
Main gas valve opens, flames ignite (30 seconds after blower)
Blower turns off when thermostat temperature is achieved


Now, here's what's happening:


Damper door opens
Pilot light clicks on
Blower turns on
Blower turns off one minute later

I know it's not an issue of gas flow, since I observed the correct firing sequence only two days ago, as well as witnessing the gas meter (which is in the same room) running during that working sequence. When the second scenario happens, the gas meter is still. Hence, my conclusion is the thermocouple or thermopile is not working correctly.

The reason I say both thermocouple and thermopile is because that's what I think is in my system. I snuck my camera underneath the sensors and saw a connection for the pilot ignite, a thermocouple that runs to the gas valve, and a thermopile that runs to the control board. Those three things are connected to a bracket that I can remove with a couple of screws.

I guess my question at this point is: Am I correct in my assessment? Do I replace both the thermocouple and thermopile, just to be safe? Or am I totally wrong? 

Here's a couple more close-ups:


----------



## user_12345a (Nov 23, 2014)

Your furnace doesn't have a thermocouple or thermopile.

It has a flame sensor and spark ignitor.

I recommend that you call a pro to properly service this unit. Reason being is that on a unit this age the heat exchanger is likely to be cracked.

I wouldn't invest much in a lennox whisperheat if it comes to needing major repairs. Most are likely 20+ years old, inefficient and cracked. i think it was the last low efficiency unit lennox produced but they got away with selling it into the 1990s because of the damper.

If you want to proceed with troubleshooting, you'll need a meter that can check resistance, ac voltage, and possibly dc micro-amps.

You would need to give us the model number of the ignition module or post a picture with the terminal labels readable.

the module will say honeywell, johnson controls or robert shaw on it.


----------



## user_12345a (Nov 23, 2014)

don't change the flame sensor or ignitor, the problem is most likely upstream of those.


----------



## yuri (Nov 29, 2008)

It can be a dozen different problems with that furnace.

I have worked on it for 20+ yrs and know it like the back of my hand.

It has a pilot burner with a spark ignition and a flame sensor which converts a AC current to DC as it jumps thru the pilot flame.

It should spark and ignite the pilot and then within a few seconds the burner should ignite. If not it could be a dirty flame sensor or the pilot burner is warped and corroded or a faulty ignition control which reads the flame signal or the gas valve sticking closed etc.

It has a BCC blower control centre board which gets energized with lighting the pilot and a timer in it for the fan.

Seems like you are not getting the burner lit and the fan is not the issue.

It is a VERY difficult unit to work on to get the pilot burner out and you need a DC microamp meter to test the flame signal.

It can be repaired by a Lennox Pro but it is expensive and a losing money pit. I would replace it.


----------



## tycho1974 (Oct 26, 2016)

Wow, thanks for the fast responses! I wasn't expecting such quickness.

And thanks for clearing up the terminology; on previous units I had experience with, I dealth with thermocouples and thermopiles, and I thought that would hold true on this one. I'd rather not replace this unit this year, since we're planning on building an addition to the house soon. I'd prefer to replace the furnace and water heater at that time. 

So do I have any realistic options for servicing the unit to have it working one last winter? Best case scenario, in my mind, is if the issue is just with a bad flame sensor that needs to be replaced. That should carry it through into 2017, yes?

Here's a couple more photos if it helps:


----------



## tycho1974 (Oct 26, 2016)

Also a quick video of the pilot light ignition sequence. It clicks like this for about thirty seconds. (I don't know why the video is rotated 90 degrees.)

https://dl.dropboxusercontent.com/u/14653556/Forum Attachments/2016-10-25 20.50.26.mov


----------



## user_12345a (Nov 23, 2014)

The video is barely watchable in it's current form, well unless u have a quad core cpu which i don't.

The spark continues after the pilot lights.

If you have a meter, put it in series with the wire going to the flame sensor and set it to dc micro-amps.










start the furnace and check the reading after the pilot lights.

Another thing to check is the physical size of the pilot; if the orifice is dirty it won't shoot out and engulf the flame sensor. It will be more like a candle and have a weak looking flame.

The pilot should have a strong blue colour, not a light blue with yellow at the end.

The flame sensor is just a piece of metal - u can clean it with sand-paper if need be. You don't need to change it unless the ceramic is cracked.



If the flame sense signal is low, you'll have to pull the pilot assemble which will be a huge pain; it will be extra-difficult with that silly burner box/damper lennox designed the furnace with.



Would have to clean the pilot orifice if it's dirty, along with the flame sensor.

Other problems can cause this like a bad ground or bad connection. Even a bad module can cause this.


-----------------------
About repairing vs replacing:

I can appreciate not wanting to replace before doing an addition because the required capacity may be different.

Keep in mind that you can't just add vents to an existing duct system and expect it to work right; the trunk lines will have to be enlarged to accommodate any significant addition.

Check the serial number to determine it's age. The year is the 3rd and 4th digit.

This unit could be made anywhere from the late 80s to even 2000.


----------



## user_12345a (Nov 23, 2014)

some info here -> http://www.achrnews.com/articles/98085-troubleshooting-a-flame-rectification-system


----------



## yuri (Nov 29, 2008)

It could be a dirty flame sensor and I have had to change lots of pilot burners with the sensor. The hood gets warped from many years of being heated and cooled and gets too far away from the sensor.

That furnace can have a serious problem with the gas valve developing a short between the MV and PV, main valve and pilot valve coils. When that happens it turns on the main burners at the same time the spark starts and you get a explosion. Like turning on the gas to a BBQ with the lid closed and then firing a match inside.

No way to know what the problem is until you remove and clean the flame sensor and you use clean steel wool or #800 emory paper not sandpaper.


----------



## user_12345a (Nov 23, 2014)

tips for that as i've done it:

1. Shut the gas off before doing anything
2. use only a open end wrench, no vice grips, nothing adjustable
3. do not force anything, if the brass nut isn't catching you're doing something wrong
4. disconnect the pilot line at the gas valve first if u can't disconnect it at the pilot assembly in place. u disconnect the line from the valve, pull the pilot assembly, then disconnect it from the assembly

5. test all connections with soap/water when finished. disconnect the wire connected to mv, let the pilot light and put soap/water solutions on both connections, check for bubbles.

6. pilot line is very easy to kink, it's not like copper pipe. don't bend it around.
5.


----------



## tycho1974 (Oct 26, 2016)

Thanks for these tips. I just got home and got back in there, and this is what I found:


Serial number indicates a production year of 1994, so 22 years old at this point.
The igniter controller is a Honeywell S8670K.
After failing to ignite the main burners, the controller LED flashes twice; according to the manual I found online, this indicates that the pilot flame was not detected.
So again, best case scenario would seem to be that the flame sensor is not working properly, or that the pilot flame is too weak to trigger the sensor. My first step, then, would be to test the sensor as suggested by @user_12345a. I'm thinking that I'll end up having to clean/replace the flame sensor, and check the pilot flame intensity, correct?

*I did notice this time that during testing, the pilot clicked for 10 seconds, ignited, stopped clicking for 3 seconds, then started clicking again. Don't know what that's about.




















(Please excuse the red wash on that GIF - I was covering the LED light with my finger.)


----------



## user_12345a (Nov 23, 2014)

if the flame is weak, it's because the orifice is plugged. 

i'm 90% sure that it's a weak signal -> next step would be to pull the entire pilot assembly and clean the flame sensor/orifice. do the test if you have the meter, otherwise don't bother.

the orifice if it's crimpted to the metal tube and be cleaned by inserting something very thin, like a room bristle. if u insert something thicker the hole will be enlarged.

yuri mentioned that the burner may be warped/has to be replaced. if it comes to needing parts the unit should be scrapped.

if you want to run it for another year, fine. get good monoxide alarms with digital display in this case. (the ones without display only go off when you're already poisoned, the display gives an early visual warning)

heat exchanger likely cracked unless it's been replaced already. the cracks are probably closed but could open up at any time. a tech would most likely condemn the furnace and force u to replace.


----------



## yuri (Nov 29, 2008)

I would order a new pilot burner and flame sensor from Cozyparts.com and replace them.

Be prepared for a very difficult job to remove it. I had to invent special wrenches ( box end with a slot cut in it ) to slip over the pilot tubing to unscrew it from the burner. VERY easy to have gas leaks if you don't get them perfect. I have never cleaned a pilot orifice on one of them as you need special orifice bits. That is kinda a trade urban myth. 25-30 yrs ago they unscrewed from the burner and you could clean them. Now they are cheap pressed aluminum orifices and not meant to be cleaned. That unit operates on a VERY tiny flame current around 1 micro amp and is very finicky to the shape and size of the pilot flame and grounding. That is why I replace the pilot burner and flame sensor.


----------



## tycho1974 (Oct 26, 2016)

So I was able to detach the mounting bracket holding the pilot igniter, the flame sensor, and the pilot gas line, but due to the rigidity of the gas line (aluminum tube) and the lack of physical space in the furnace (it's only 3 burners), I was not able to remove the flame sensor to check/clean/replace it. I have a guy coming in the morning to take a look at it, so hopefully he can get that thing out to see what he can see.

Thanks for your help so far, and I'll be back with updates. (I like closure.)


----------



## yuri (Nov 29, 2008)

Good for you, it is not a easy unit to work on but it was hugely successful for Lennox as it is VERY quiet compared to a furnace with a ventor/exhaust fan.

It may work with just cleaning the flame sensor but it may die half way thru the Winter if the pilot burner is in poor shape which it must be after 22 yrs. I replace both and it extends the life nicely.


----------



## user_12345a (Nov 23, 2014)

Good luck. if the tech finds cracks you'll have to replace.

u pretty much have to undo the pilot gas line and take the assembly out of the furnace to properly work on it.



> Good for you, it is not a easy unit to work on but it was hugely successful for Lennox as it is VERY quiet compared to a furnace with a ventor/exhaust fan.


successful "for lennox", not for the techs who have to work on them or the homeowners having to shell out $$$$ because the heat exchanger cracked prematurely.


----------



## yuri (Nov 29, 2008)

The biggest joke of all time is those cracks are HAIRLINE cracks and I have never had one open up enough to even cause flame disturbance.

There are 3 categories of cracks.

Ones that can be there for many years and cause no problems and other brands have them also.

Ones that open open when heated and then you get flame disturbance.

Others that have split open and you get flames rolling out the front.

A big cash cow for dealers to charge labor to replace them when they are not even causing problems. Yeah yeah the code may say it is a issue but in the real world nobody has been harmed that I have ever heard of by one of them.

I don't go on a witch hunt for them.


----------



## tycho1974 (Oct 26, 2016)

All right, so it turns out that it was exactly what I thought it was: a bad flame sensor.

My technician removed the one thing I couldn't get off (the top cover of the section that holds the damper) and was able to remove the bracket holding the pilot, pilot gas line, and flame sensor. He replaced the flame sensor, gave the pilot a little cleaning and re-installed everything.

Testing the unit after replacing the flame sensor resulted in a much faster pilot to main burner ignition sequence. Previously the sequence was Pilot->Blower->Burners, with about thirty seconds in between each step. Now, the sequence is Pilot->Burners->Blower, with only five to seven seconds between steps. Examining the flames from the main burners revealed nothing unusual, both in terms of flame color and "waviness", so it doesn't appear that the heat exchange is cracked. Total cost was only a hundred clams.

Hopefully, the unit will last me at least through the winter, and now that it's operating more efficiently I think I have a good shot at that. Thanks again for your help and advice, it's been invaluable - because I was able to accurately describe the problem to the technician ahead of time, he was able to bring the appropriate replacement hardware and fix it on the spot. One thousand internet points for everybody!


----------



## yuri (Nov 29, 2008)

Glad you got it going.:vs_karate:


----------



## supers05 (May 23, 2015)

yuri said:


> The biggest joke of all time is those cracks are HAIRLINE cracks and I have never had one open up enough to even cause flame disturbance.
> 
> There are 3 categories of cracks.
> 
> ...


I totally agree. However, with the way liability is here, we can't afford to look the other way. We really have no choice but to look for those cracks and condemn. We've had contractors sour over losing business call in "anonymous" tips. (luckly it's always backfired on them) 

Those were the days when Lennox made half decent appliances that lasted a few decades. I've lost count how many heat exchangers I've replaced under warranty now this year alone.....

Cheers!


----------



## user_12345a (Nov 23, 2014)

i doubt that any manufacturer in this industry makes decent products that will last 20 to 30 years any more. it's not just lennox, granted i don't know if you've seen higher failure rate with lennox than others.


----------



## yuri (Nov 29, 2008)

Yeah, BUT I can look at it today and it may be fine and tomorrow it cracks.

No way the Dept of Labor or authorities can prove I was negligent. Unless it is grossly split open or there are obvious signs of long term flame rollout it can split 5 mins after I leave and it is not my problem. The cracks are so far in around the S bends and you need a special camera and techniques to find them. We even had guys spraying water over the heat exchanger and sticking a camera in to find them. Some company came out with a kit for that and sold it. Did not go well with the Dept of Labor where I am as they want to witness it and see it if the customer complains and wants a second opinion. Lots of scams possible where people can get told the heat exchanger is cracked and it is not but they don't get to see it. Where I am they can get a 2nd opinion from the gas co if they feel suspicious.

Our OP has a 22 yr old unit that probably has cracks but he can drive it till the day it dies or costs too much to repair and probably will be fine with it IMO. Not saying it should not be changed if a tech finds them but not all do or go on some witch hunt to find them. When you got 10 calls backed up on you and it is -40F with a 30 mph wind you are not going to hunt for cracks on every job. Just get the heat working and leave.

Any heat exchanger over 20 yrs can split wide open 5 mins after you leave due to metallurgy issues from repetitive heat/cool expand/contract cycles.

IMO changing those heat exchanger for cracks that will never cause a problem is a cash cow and in real world situations they have never been a problem. Of course a crack is a crack and techs like changing them and it is a cash cow for dealers.

Actually they are a HUGE pain in the azz to change unless you are doing the small ones. I leave it to the apprentices and junior techs and I do the real big boy serious troubleshooting.


----------



## supers05 (May 23, 2015)

user_12345a said:


> i doubt that any manufacturer in this industry makes decent products that will last 20 to 30 years any more. it's not just lennox, granted i don't know if you've seen higher failure rate with lennox than others.


I've had my doubts with one other company lately..... But they are going through a product re-design on the electrical side.... yaaaayyy (i hope that i was sarcastic enough) 

As for L, so far it's mainly there commercial stuff. Certainly, you'd expect their products to last their warranty, and life expectancy. I'm not talking decades, I'm talking years measured with fingers on one hand, across dozens of locations. Everything engineered, signed, stamped, approved, the whole nine yards. Heating and cooling. Can't blame airflow or electricity problems on everything. 

Essentially, we refuse to install them now I'm commercial settings. Their residential stuff seems on par with the industry, but that's mostly hearsay for me. 

Cheers!


----------



## yuri (Nov 29, 2008)

Daikin and Rheem seem to be selling s lot of RTU's where I am. Maybe they are priced better than Lennox and Carrier, I don't know.

Lots of Yorks being sold too. I don't do RTU's or care anymore.:vs_no_no_no:


----------



## supers05 (May 23, 2015)

If it's a hairline, it's unlikely that I'm seeing it anyways, since a cell for me is the size of the side of my truck. Then you're in an impossible position to see the cells. Lol. (one of the backfires I mentioned above, took a smokebomb test, 3 techs, 2 agents, and 2 hours to prove a hairline crack from a combustion test. Forklifts were putting out a documented 10x the CO then our MUA anyways. They got the bill, not us.) 

We take pictures of all of ours, and send it to the customer. Usually along with a pen sticking out of it for scale. I agree, people make a much bigger deal out of hairline cracks then they need to be. I just hate the liability always hanging over my head with it. The only part of this trade that I don't like. 

Cheers!


----------



## supers05 (May 23, 2015)

yuri said:


> The biggest joke of all time is those cracks are HAIRLINE cracks and I have never had one open up enough to even cause flame disturbance.
> ....


Was watching videos completely unrelated, and stumbled on this one and thought of you yuri. [emoji6] 
Hairlines are a complete joke. While I don't like the actual words that he uses, he's going in the right direction with the explanation. Proves really well how little the hairlines leak compared to the seams. The heat exchanger is supposed to be in a slight negative anyways, with it being completely natural at the burner. 

OP. Don't loose to much sleep over it, the video does a good job at showing that. 






Cheers!


----------



## user_12345a (Nov 23, 2014)

He mentioned filling the cells with water and negative pressure, etc.

The reality is that when those heat exchangers warm up the metal forms a seal when it expands.

where cracks can open up as the metal expands.

Hairline cracks aren't a big deal, but if they're used as an excuse to take a 20+ year old g20 natural draft furnace out of service that's fine.


----------



## supers05 (May 23, 2015)

user_12345a said:


> He mentioned filling the cells with water and negative pressure, etc.
> 
> The reality is that when those heat exchangers warm up the metal forms a seal when it expands.
> 
> ...


To be honest, I'm not complaining about the hours. It's good business. Big holes in heat exchangers cause flame and ignition problems. No doubt about it. I don't like fixing them at -20*C.

But, had I been a home owner before I got into this racket, and saw a tech do that, just to condemn a condemn my furnace, (not saying that's what the guy in the video did, he's just an water example) I'd send him off just to find someone else. Even if that someone what was more expensive, just because that original guy was such a jerk. 

I do a combustion test, and take a look at the heat exchanger from the plenum. If I can see anything, or the test has bad numbers, it's condemned if appropriate and a quote given. Some of those guys are just jerks. (i suspect that the guy in the video was the second opinion, and is more on our side.)

PS. He said positive pressure at least once. Maybe I misheard. I just notched it up to mispoken words, nothing more. 

Cheers!


----------



## tycho1974 (Oct 26, 2016)

Just thought I'd put up some photos of the old flame sensor, so others can get a sense of what a "worn" sensor looks like. I'll admit my untrained eyes don't see much wear or damage on here, but now I at least have a frame of reference...


----------



## user_12345a (Nov 23, 2014)

flame sensors don't go bad, it's just a piece of metal which needs to be cleaned with sand paper or steel wool.


----------



## yuri (Nov 29, 2008)

You can clean it with clean steel wool or #800 emory paper but not cheap sandpaper or it will get scratched.


----------

