Armstrong EG6A125DC15-13 Roll Out Switch

Sorry in advance for the length of this post, but I wanted to try to be as specific as possible on this problem.
I have two 16+ year old Armstrong natural gas furnaces (model number in subject line above) for my residence. Both identical spark ignition, 125,000 BTU 5-burner units.
I had a soot build up problem with the lower level unit (the one that is used most frequently) that caused the flame on the left-most burner to slightly roll out from the heat exchanger chamber, so I called a reputable local service company to come out and clean both of the units.
They removed the flue and front panel and then thoroughly cleaned the sooted up heat exchanger and flue vent. (They found the heat exchange cavity by the leftmost burner completely blocked with soot). They also removed and cleaned all the burners too and then re-assembled everything. In this process, they also discovered that the air mixture controls for the 5 burners were shut down completely and opened them up (all the way to max settings) to let the burners "breathe" properly. The flame tip color turned a much deeper blue and the dark blue "inner" flame mantles appeared to go down to about 3/4" long. The good news here was that this stopped the orange tipped flame from rolling out of the combustion chamber and resulted in a noticeably hotter flame. (I've also been monitoring CO in the area around the furnaces and it has gone from 20+ PPM when the furnace was running to 0 PPM now.)
Unfortunately, changing the air mixture seems to have introduced a new problem. Now during extended runs of this furnace (for example when coming up to temperature in the AM after a setback period the previous night), the flue roll out switch trips shutting down the system. When this happens it requires a manual reset of the roll out switch button. If the furnace is simply "cycling" to maintain temperature, then it does not seem to trip and everything is fine. The drafting on the furnace seems to be good so I suspected that it was just burning too hot for the switch.
Thinking this was possibly a weak/old/failing roll out switch, I swapped the switch with the one in my upstairs furnace, but this did not fix the problem and it still tripped just the same (and the upstairs unit which now has the switch from the downstairs unit did not trip). At this point, I have tried backing off the air mixture to about 50% from being wide open on all 5 burners, but this too seems to have had no affect.
The only thing that I've found that does seem to prevent this switch from tripping is to manually feather the gas shut off valve to the point where I can observe a noticeable reduction in the flame height on the 5 burners.
I'd appreciate thoughts on what is happening here. I do not believe it is an issue with a blocked flue since both furnaces were thoroughly cleaned and share the same flue stack/chimney and the upstairs unit does not have this same problem. I suspect it may be that the air/fuel mixture is still not correct or possibly that the gas pressure from the gas valve to the burner orifices on the lower level furnace may be set too high. (I am not sure how these are set.) My service company is stumped and after being charged for two trips, I am not anxious to have them come back till I understand what is happening here.
Thoughts and ideas on what I can look at or try are very much appreciated. I know these units are only about 65% efficient and getting old, but replacement at this time is not an option since they are otherwise still running well!
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Replacement time is *ALWAYS* an option. From my personal experience with my customers, its not unusual for their utility bills to drop as much as 60% or more with a new system. Changing to a correctly sized 80+ furnace will make a huge difference, and even more so for a 90+ furnace.
You might have to replace it sooner than you anticipated anyway... One or 2 cells sooting up, is a bad thing.. I would suggest that the heat exchanger be inspected for cracks... bet ya find some. Armstrong's paper thin, clamshell, heat exchangers(especially the older ones) are not noted for their longevity. When the cracks are found, then your not gonna have much of a choice in the matter other than spend the money and replace it or be cold.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Noon-air (love that handle),
Thanks for your comments. The service company did use a camera and said there were no obvious cracks and that the unit appeared to otherwise be in good condition.
I know there would be operating savings, but can't get past the cost estimate I received (4 figures) since I have two furnaces and 2 central A/C units to replace and high efficiency costs a lot of money!
What I was really hoping was that someone could shed some light on why the thing is running "too hot" now that the air mixture has been increased. Shouldn't the temp still be regulated by the amount of natural gas that is provided by the electric valve? Why should I need to decrease the air mixture, and in effect make the unit run LESS efficiently by throwing unburned fuel up the flue?
All I can figure is that the gas pressure getting to the burners are too high since the orifices have not changed since it was installed. But the service company seems to think these are permanently regulated and not really adjustable in the field. I have accomplished the same end result by throttling back the main shut off gas valve, but needing to do this means there is another problem somewhere else. Other thoughts are appreciated.
Bob

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Noonie's answer is always to change out the equipment.
Call a company that has the tools and knowledge to check what you actually have. Draft gauge, combustion analyzer, manometer etc.
You need to keep your fingers out of the equipment.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Noon is absolutely correct - odds are better than not that there is a crack in the exchanger(s). We carried Armstrong as a secondary for years until issues with their heat exchangers outweighed their willingness to correct them. Just like Janitrol/Goodman/Amana - if I see an Armstrong still in service any time I'm in the field - irrespective of the season I dig into the exchanger. If the cells have not already been replaced, a compromise is found in 3 of 5 pieces of equipment, I would guess.
Aside for that 16 year old equipment is costing you more to operate than it would be to replace with upgraded equipment in the big picture.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I'm sorry, I thought the tread was about the flame roll out not the blocked flue switch. Can you clarify????
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Feb 16, 7:53pm, snipped-for-privacy@mailcan.com wrote:

First, I'm concerned the furnace is oversized for application which would cause short cycling, moisture in heat exchanger, rusting of burner and sooting of cells.
Have you had a Manual J, Heat/Load Loss Calc done on 1st floor? If not, I highly recommend it. Any reputable contractor will do this during their estimate on a new furnace, it is becoming law in a many states.
You could easily tell if your furnace is short cycling by watching it when you turn your heat up high, say 10 degress. Watch the flames, do they shut down and blower continue to run with the thermostat unsatisfied? If so, your furnace is short cycle, overheating. After enough time, this can cause moisture to build up in the heat exchanger just like only taking short trips in the car to the grocery store can rust out your car's exhaust system.
For a roll out switch to trip, it happens for couple of reasons. What I am hearing is that instead of rollout switch being licked by flames rolling out of combustion chambers, the heat exchanger is overheating, transferring heat into the front plate and then into the bracket that holds the rollout switch then tripping the switch. (Unrelated: Rheem had a problem on particular furance where there was a Service Alert to replace the bracket on their rollout switches for this problem--not a Rheem dealer, but you techs know--we service all makes and models).
Another way to tell if enough air is getting past heat exchanger is by doing a CFM test. By this you measure the return air temperature and supply air temperature (supply temp minus return temp). This is called deltaT (temp differential). Take bonnet BTU of furnace (not input but output, for example: input BTU, 125k btu furance multiplied by efficency, say 65% or .65) divided by deltaT that has been multiplied by 1.08. CFM for 125k BTU, I'm hoping you have 1600 or better for your furnace.
bonnet BTU CFM = _____________________ deltaT x 1.08
If not moving not enough air, get the Manual J. If furnace is sized properly for house, then insist on Manual D...and always change your filter. (may I suggest you avoid the pleated filters at this stage??)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@mailcan.com wrote:

Wow, such detail for such a interesting quandary. Are you sure of all that? Perhaps you want to just camp at his house for the afternoon.
Could be something as simple as leaving the blower door on the furnace ajar. Combustion air vent [inlet] blockage for the equipment closet? Could be something as simple as a failed firebox. Doubt it's the switch. Doubt the firebox is seeing to much heat [transferring it to the switch]. If the firebox was sooting, and, there was flame impingement, it can have a rupture. A rupture that doesn't show on visual. It could open after heating a bit causing flames to roll out. [There's a reason the Mfg. put the switch in the first place.]
--
Zyp



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
To clarify, the switch I am having trouble with is at the top of the unit nearest to the exhaust flue. It is called a "roll out" switch in the schematic drawing, so I called it the same. It is identical to the "roll out" switch at the front and slightly above the burner elements. That switch seems to be operating fine since it is not tripping.
Also, someone suggested the furnace may be short cycling, but this is not the case either. The thermostat calls for heat, the pilot gets gas, the electronic ignition kicks in and the pilot lights, then the thermocouple senses the flame and turns on gas to the burners which ignite. They burn for about 20-30 seconds and the blower fan kicks in. The gas burners and blower run till temperature is reached and the thermostat shuts off, the gas valve closes and the burners shut down. The blower fan runs for a few minutes and then shuts off when the low temp limit is reached.
I just do not understand why the sheet metal at the top near the exhaust flue gets hot enough to shut down the unit when the manual shut off valve is fully opened. Hope this clarifies the situation.
Bob

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How long are you going to keep screwing with it before you call somebody that knows WTF they are doing??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bob Shuman wrote:

That's a lot clearer Bob;
The control adjacent to the flu stack is a "draft safeguard switch." It's purpose in life is to prevent back drafts. You have a flue problem. Go see if the flu stack is high enough [i.e. 24" above any projection within 10 feet of the stack.] If you have prevailing winds, it could be "back drafting" long enough to trip the control. You might have to many turns in the flu stack as well. It must not have more than one 90 degree turn meaning 45 degree turns are ok. It must have a buoyant head, meaning the stack leaving the appliance must have at least 12" of vertical before taking turns [unless the appliance is lying in a horizontal position.] See the Mfg.'s instructions and for advice.
If anything, call a certified NATE technician. He / she will see the problem fairly quick.
Zyp
--
Zyp



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Zyp & ftwhd,
Thanks for your helpful comments. I'll take it from here.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 14 Feb 2008 09:52:20 -0600, "Bob Shuman"

WOW! Simply amazing! I hate to be so blunt but everyone here knows thats the way I do it so try not to take this too personal. Unfortunately, I cant quite figure out who is dumber. Is it the service company that came out and cleaned out all that soot? OR Is it the homeowner that has to keep resetting a MANUAL RESET ROLL-OUT switch? When you find soot you MUST find out WHY it was produced. It seems that "someone" didnt. Too bad. When "someone" has to reset a "manual reset roll-out switch" one must determine, WHY is this having to be reset? Both clues (the soot and the manual resetting) can be VERY dangerous conditions and even life endangering. You most likely have a cracked heat exchanger. Time to break open the piggy bank and get some properly sized high efficiency furnaces. Bubba
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Feb 14, 10:52am, "Bob Shuman" < snipped-for-privacy@removethis.alcatel- lucent.com> wrote:

You got a draft issue. Either the flue is still stopped up somewhere or there is not enough fresh air available to supply the unit. Other possibility is that your flue never was adequate and the original installed dicked with your mixture in an effort to mask the flue problem.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is a follow up to a 6+ month old post (attached below):
I wanted to follow up my original post in case anyone reads this thread to let them know that I have resolved this problem. I went ahead and replaced the heat exchanger and the unit is now drafting properly (zero CO emissions and match flame test look good after extended runs) and the roll out switch no longer kicks in to shut down the furnace. Other than finding the part and it being fairly heavy and somewhat labor intensive, the replacement was actually pretty straight forward.
After removing the old HE, I looked it over, but could not see any obvious cracks or leaks. (It actually looked to be in great condition after 18 years of use). Given that it only exhibited this (leaking) behavior after the burners had run for several minutes and the HE had warmed up, I must assume that one of the crimps or welds had separated and it leaked only after the metal expanded.
Thanks to all in this news group who had replied and suggested this as the cause.
Bob
news:...

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Cue the crickets..........
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.