Re: 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

> 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.