Armstrong EG6A125DC15-13 Roll Out Switch Tripping

Reply

  #1  
Old 02-14-08, 07:53 AM
Member
Thread Starter
Join Date: Feb 2008
Posts: 3
Upvotes: 0
Received 0 Votes on 0 Posts
Armstrong EG6A125DC15-13 Roll Out Switch Tripping

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
 
Sponsored Links
  #2  
Old 02-14-08, 01:09 PM
Member
Join Date: Oct 2005
Location: USA
Posts: 1,076
Upvotes: 0
Received 0 Votes on 0 Posts
Perhaps the furnace is being over fired (gas valve adjustment too high). Best to let a pro check that with a manometer.

Another possibility is a cracked heat exchanger. At that age, anything is possible.
 
  #3  
Old 02-14-08, 04:01 PM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Upvotes: 0
Received 0 Votes on 0 Posts
The guys who came to service your unit indeed fixed one problem at the expense, perhaps, of creating a new one.

soot comes about due to a lack of primary air...this in turn could be caused by one of two things: (1) flappers that are almost completely shut-off (the air mixture controls as you call them), or (2) the furnace being in a room that is airtight and does not have enough air for prolonged combustion.

fully opening the flappers overfeeds oxygen to the fire. This immediately brings an increase in the temperature of the combustion gasses, so it is no wonder that your rollout is tripping...PLUS...too lean a fuel mixture (too much air) has de effect of having the efficiency of the furnace take a dive (more is not necessarily better in this field).

Did the guys use a combustion efficiency test to check the efficiency of the furnace as they opened the flappers?
It is not about opening them fully but up to a point, the point of top efficiency for this particular unit.

The flappers, furthermore, come factory set. Playing devils advocate, it is possible that when the tech was cleaning the burners accidentally may have gotten one of the flappers out of its original position and ended up showing as "closed".

At any rate, these flappers should be reset, towards a less open position...incrementally...until the unit's efficiency (as stated by the manufacturer and verified by the combustion efficiency tester) is reached. That will lower the temperature of the flame and you won't have your rollout switch tripping anymore
 

Last edited by pflor; 02-14-08 at 05:10 PM.
  #4  
Old 02-15-08, 08:38 PM
Member
Thread Starter
Join Date: Feb 2008
Posts: 3
Upvotes: 0
Received 0 Votes on 0 Posts
Jim and Pflor,

Thanks for the feedback. I agree with you completely. I think that this service company solved one problem and created another.

Can you explain in more detail the reasoning behind the efficiency decreasing and the temperature of the exhaust increasing when too much air is allowed to mix with the gas source?

Logic would tell me that the gas pressure and orifices are fixed to the burners, so the flow of gas would also be "fixed" by these factors. As such, I would think that the highest combustion efficiency would be reached when the flame was the hottest. You indicate that efficiency decreases as more air is supplied ...

Thanks for taking the time to help educate me. I'm not sure what I am going to do at this point. I can't leave the gas valve throttled back indefinitely, but I also don't think the service company I've been using has a clue on how to adjust these correctly or measure the gas pressure.

Bob
 
  #5  
Old 02-15-08, 10:16 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Upvotes: 0
Received 0 Votes on 0 Posts
Flappers in the furnace room! Does this guy's wife know there are wild women from the 1920s down there?!


Well. Too much primary air can cool down the flames, causing various problems, and can even cause excessive carbon monoxide to be produced if the flames get cooled off enough.

I agree that it sounds like the furnace is being overfired, probably causing enough radiant heat to cause the rollout switches to open. That would be unusual, but possible.


You do want to be sure there isn't some actual spillage of combustion gasses out the front of the burner area, which is the usual cause for a flame rollout switch to open. An overfired furnace or a vent system that's not allowing the combustion gasses to vent properly could cause that.

You need to have a good repairman set up the furnace properly after all the seat of the pants adjustments that have been done. I careful inspection of possible flame rollout and radiant heat problems would be a good place to start, followed by carefully setting the furnace input to the correct level, probably by clocking the meter. Then setting the primary air shutters (NOT flappers!) to an opening that gives a proper gas flame.

That probably wouln't take long to do, IF you get a competent repairman to do the job. I'd concentrate on that as your task.
 
  #6  
Old 02-16-08, 03:16 AM
Member
Thread Starter
Join Date: Feb 2008
Posts: 3
Upvotes: 0
Received 0 Votes on 0 Posts
Seattle,

I think this is good advice. I have been monitoring the CO using a digital readout sesnor located about 15 feet from the furnaces. Before the thorough cleaning, (When I had the soot problem), I observed a 20 PPM reading (and a peak of 37 PPM)while that furnace ran. Once the furnace was cleaned and the shutters were opened, I have seen a zero reading (0 peak) for the last two weeks. Drafting up the flue looks very good as evidenced by a flame test.

I do think the burners are running too hot. I have most of the floor vents in the lower level opened and there is a new filter in the unit too, so do not believe it is an air flow/blower issue. This leaves me to suspect that the shutters are still not adjusted right OR it is getting too much gas.

I can reduce the air misture further, but worry that shutting these down too far will cause a return of the sooting problem.

Thanks.

Bob
 
  #7  
Old 02-16-08, 11:13 AM
pflor's Avatar
Member
Join Date: Dec 2007
Location: U.S.A.
Posts: 1,127
Upvotes: 0
Received 0 Votes on 0 Posts
Talking flappers

with my apologies, guys
The correct name is "Primay Air Shutters"...not flappers.

Combustion gases are to circulate through the heat exchanger "exchanging" heat with the heat exchanger. They do this as they move through the heat exchanger surfaces on their way out to the smoke pipe and up the chimney.

If too much of it is fed, it's kind'a they'll be rushed thru the combustion chamber, not staying there long enough in the heat exchanger to give off their heat and the consequence is elevated temperatures.

It does sound like a paradox, that more air would bring up the temperature of the combustion gases.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: