Furnace burner shuts off intermittently


  #1  
Old 12-31-09, 07:12 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Furnace burner shuts off intermittently

Hello to all,

I have an intermittent issue with my forced air gas furnace. The furnace is an older high effiency unit made by INTER-CITY PRODUCTS CORP, Model DGHH075A012IN, Serial No D92157666.

Quite often the burner will shut down in the middle of a heating cycle. The draft inducer motor continues to run during this period and after a few minutes the burner will then re-ignite and finishing heating until it reaches the thermostat set point. During this period I have verified that my pressure switches and roll out switch are closed and supplying 24v to my Honeywell S8600M Ignition Module. I have also replaced this module thinking it was the problem.

I think it may be a feedback issue with my ignitor, but I am not sure. The ignitor is like a spark plug and has a single large insulated wire going to it. I believe a small amount of current is fed back to the module through this wire while the burner is on. Perhaps this gets interrupted sometimes? I'm not sure how to check for this.

Another important note, when this problem occurs I can easily resolve the issue by turning off the furnace and turning it back on. The furnace will always immediately re-ignite after this.

Any help or suggestions on things to check would be much appreciated. Thank you and Happy New Year!
 
  #2  
Old 12-31-09, 07:36 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Have you checked to see if the limit switch is opening? That you can switch the power on/off and get the burners back on suggests that it isn't the limit switch, but I'd check to be sure.


The way to test the Honeywell module for a flame detection fault is to measure the DC current flowing back to the ground terminal on the module.

The current should be 3-5 microamps, and the module will probably work OK with currents of 1 microamp. Less than that it will probably work intermittently as you describe or not at all.
 
  #3  
Old 01-01-10, 05:17 PM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thank you for your suggestions. I will verify the limit switch is not open during the intermittent burner shutdown. This is easy to test.

I need a little more guidance on testing the flame detection fault however. The Honeywell module operates at 24 VAC. My amp meter only reads DC current. Where would I hook up my amp meter to check this? Thanks.
 
  #4  
Old 01-07-10, 05:53 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Intermittent Burner Shutdown

I have verified that my limit switch is still closed when the burner shuts down. So to recap, my furnace burner and main blower will shutdown temporarily sometimes before reaching the thermostat set point. The draft inducer motor stays on and my limit switch, pressure switches, and roll out switch are all closed. I have no voltage to my gas valve during this period. After about 5 minutes (and this amount of time seems to be very consistant) the controller suddenly decides to send voltage to the gas valve, the pilot lights and all is well again. If I power off the furnace during this period and turn it back on, the furnace ALWAYS starts back up immediately.

This problem is very intermittent and does not happen all the time, but it does occur a few times daily though. Most of the time my furnace operates correctly throughtout the entire heating cycle. The furnace is about 20 years old, but has never had this problem until this season.

Any suggestions what could be going on here?
 
  #5  
Old 01-07-10, 09:02 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by gmc1972
I have no voltage to my gas valve during this period. After about 5 minutes (and this amount of time seems to be very consistant) the controller suddenly decides to send voltage to the gas valve, the pilot lights and all is well again.

There seems to be a contradiction here. In sentence one you say there is no voltage to the gas valve, while in the second sentence you say voltage is suddenly switched on to the gas valve by the ignition module.

Please resolve this discrepancy.
 
  #6  
Old 01-07-10, 11:54 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I'm sorry, let me try and clarify. Sometimes during a heating cycle I have an intermittent burner shutdown where the gas valve closes because the controller no longer supplies voltage to it. This burner shutdown lasts for about 5 minutes while most operating conditions are still satisified: thermostat on, limit switch closed, pressure switches closed, roll out switch closed.

After 5 minutes, the burner re-ignites and the furnace finishes heating until the thermostat set point is reached. I can clear the fault sooner by simply shutting off the furnace and turning it back on.
 
  #7  
Old 01-07-10, 02:53 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Erratic operation of the kind you describe suggests either a poor electrical connection or a bad ignition module.


I'd check to make sure you have 24 VAC properly applied to power the ignition module when it quits. That would include checking to be sure the module has a good ground as well.

If it does and it still shuts off, I'd replace the ignition module.

The basic idea is to treat the ignition module as a black box. If it has all the correct input, it should have certain outputs (keeping the gas valve energized. If it doesn't, the black box is defective.
 
  #8  
Old 01-08-10, 07:28 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I have verified that I do have 24 VAC at the ignition module when it quits. I have also replaced the ignition module and the problem still exists. There is one 24V ground wire going to this module from my Honeywell fan timer control board. Everything with this wire and the connections seem to be OK. Could there be an issue with the Honeywell fan timer board? It is p/n ST9120C 2010.
 
  #9  
Old 01-08-10, 08:31 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by gmc1972
Could there be an issue with the Honeywell fan timer board? It is p/n ST9120C 2010.


Can't see how that would be an issue.


This Honewell ignition control box uses flame rectification to verify that the pilot burner is properly lit. Checking to see if the flame rectification current is there is something that can be done.


Do you have a multimeter that measures DC microamps? You need to be able to measure down to 1/2 microamp or so, with 1,000,000 microamps = 1 amp.
 
  #10  
Old 01-08-10, 10:10 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yes, I have a multimeter that can read DC microamps. Where should this be hooked up at? I only have a single spark plug style wire going to my ignitor.
 
  #11  
Old 01-08-10, 10:14 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Measure the microamps flowing from the furnace chassis ground to the ground connection on the Honeywell ignition module.

A reading of 3-5 microamps when the burner is on is good, and should keep the burner lit. A reading of 1/2-1 microamps is marginal and would cause the burners to shut off or operate unreliably. 1-3 microamps may provide sufficient current to keep the burners lit.

You will only get a read when the burners are lit, and you need to remove the existing ground connection to the ground terminal of the ignition control for this test.
 
  #12  
Old 01-08-10, 12:52 PM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
OK, thanks! I will test this tomorrow and let you know...
 
  #13  
Old 01-11-10, 07:05 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yesterday I tried testing my flame rectification. The only problem is when I disconnect the ground connection to the Honeywell module, the burners immediately shut off. Is this normal? I cannot make a measurement unless the burners are on, correct?
 
  #14  
Old 01-13-10, 08:20 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Is it normal for the burners to shutoff when the ground connection is removed from the Honeywell ignition module? If so, how is flame rectification tested?
 
  #15  
Old 01-13-10, 09:56 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Yes, it is. An AC voltage is applied to the pilot burner eletrode, and when the flame is on a small DC current is rectified from the AC voltage and flows to ground, and thence to the G terminal on the ignition control.

You connect your ammeter between the chassis ground and the G terminal to measure that current when the flame is present.

The flame should remain on when the ammeter is connected up that way.
 

Last edited by SeattlePioneer; 01-13-10 at 10:17 AM.
  #16  
Old 01-18-10, 08:14 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I tried testing my flame rectification again last weekend. I was unable to get any microamp reading. I am not an electrical engineer so I most have done something wrong.

First of all I have two terminals on my Honeywell S8600M module that are labeled ground. Terminal 4 is labeled "GND (BURNER)" and has a green lead going to a ground terminal near my gas valve. Terminal 5 is labeled "24V (GND)" and has a yellow lead going to the fan timer board. Since I was unsure which terminal to test I tried testing both independently by hooking up my multimeter in series in-between the module terminal and furnace chassis. I had no uamp reading with this hookup.

It should be noted that the furnace would run while testing terminal 4, but the burners shut down while testing terminal 5. I also tried hooking up my multimeter in series in-between the module terminal and corresponding wire that connects to it. This did not work either.

Which terminal on my module should be tested? Do I have to hook up my multimeter differently?
 
  #17  
Old 01-18-10, 05:30 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Did you test between #4 burner wire and module terminal #4 with the wire off the terminal? If it were left on the terminal, you would not be testing in series.
 
  #18  
Old 01-18-10, 09:22 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by ecman51`
Did you test between #4 burner wire and module terminal #4 with the wire off the terminal? If it were left on the terminal, you would not be testing in series.
Ecman is correct.


Just to put a point on it, you want to disconnect the wire going to terminal 4 from the chassis ground and connect one wire from the multimeter to that wire or a chassis ground and the other wire to the multimeter to the terminal 4 Gnd Burner connection.
 
  #19  
Old 01-19-10, 11:29 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Ecman / SeattlePioneer,

First of all thanks for your help. I'm going nuts with my furnace as the burners continue to shutdown intermediately 5 or 6 times daily.

I believe my test setup was correct. I disconnected my green burner ground wire going to terminal 4 on my module and inserted my multimeter inbetween this wire and terminal 4 on the module. With this setup current has to flow through the multimeter to reach ground. I also verified my multimeter setting and test leads were setup for reading uamps. With this setup I had no reading at all while the burners were on. Can this be possible?

It should be noted that my burners continued to run when I removed my multimeter from this setup and terminal 4 was completely disconnected. Is this normal? I would have thought my burners should have shutdown without this connection.
 
  #20  
Old 01-19-10, 12:00 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
The burners should shut off immediately when the wire to ground is disconnected. I don't recall ever encountering a failure of this module to shut off u nder such conditions. It implies that the flame rectification sensor is stuck or not working.

If your multimeter was sensitive enough, you should also have been measuring 3-5 microamps DC or so ---- I presume you were checking for DC microamps?

That none were present also implies a defect in the flame rectification circuit.

I'd replace the module. These can often be had on ebay pretty cheaply.
 
  #21  
Old 01-19-10, 02:47 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Interestingly, post #13 and 19 are at odds with each other, in regards to what happens when the ground circuit is disconnected.
 
  #22  
Old 01-21-10, 05:56 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Sorry for the confusion. On post 13 I was testing terminal 5 on my module labeled "24V (GND)". On post 19 I was testing terminal 4 labeled "GND (BURNER)". Now I know to just test terminal 4 for flame rectification.

As I said before, I am not an electrical engineer so I carefully retested my flame retification last night. Here's what I found. I do have a very small amount of DC current flowing back to ground. My multimeter fluttered between 0.0 and 0.1 uamps. When I disconnected my multimeter from terminal 4 and ground, my burners did shutdown immediately until the ground circuit was closed again. I have another module so I tested this also. I had the same result. Measurements fluttered only between 0.0 and 0.1 uamps and the burners shutdown when the ground circuit was open.

If the current should be 3-5 uamps, my system is far below normal. This seems like a logical reason why my furnace burners shutdown intermittently. What would cause this low amount of current feedback? How can this be corrected? A different module did not improve this.
 
  #23  
Old 01-21-10, 07:30 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by gmc1972

If the current should be 3-5 uamps, my system is far below normal. This seems like a logical reason why my furnace burners shutdown intermittently. What would cause this low amount of current feedback? How can this be corrected? A different module did not improve this.


You need to have a good connection to ground for the module. Often the pilot burner has a ground wire as well which you might check for a good connection.

Also, the Honeywell pilot assembly typically acts as the flame sensor. A portion of the pilot flame should be striking the metal portion of the pilot assembly, and that could get coated with oxides and need to be cleaned with a wire brush.

Try those fixes and see if it brings your microamp readings up.
 
  #24  
Old 01-21-10, 11:26 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I know my pilot burner does not have any direct ground wire going to it, but I will try and clean it this weekend. I'll let you know how this works. Thank you so much for all your help!
 
  #25  
Old 01-25-10, 08:01 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yesterday I removed my pilot burner assembly to clean and inspect it. This ended up being quite a big job because I had to remove my entire burner assembly to access the pilot burner. Upon inspection the electrode and ground plate were not very dirty, just some slight signs of surface rust and carbon buildup from the ignition process. I cleaned these up as best I could with fine sandpaper and a wire brush.

After putting everything back together I retested my flame rectification. The pilot burner cleaning made no difference, my measurement was still fluttering only between 0.0 and 0.1 uamps of current.

My burner ground wire from my ignition module goes to a spade connector located on my gas valve assembly. From there the ground signal is carried through the gas plumbing going to the pilot burner assembly. I tested my resistance between the spade terminal and pilot burner ground plate and measured about 7.6 ohms of resistance. Is this normal or should this value be lower? Should I try adding an additional ground wire directly to the pilot burner?

Any other suggestions that could improve my flame rectification? My burners continue to shutdown intermittently.
 
  #26  
Old 01-25-10, 05:33 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Is there enough pilot flame hitting metal down at the pilot assembly, and that it is all de-oxidized, so that small dc current can get carried through the assembly? - which then in turn comes out that spade by the gas valve, then takes the wire to the control module.
 
  #27  
Old 01-26-10, 07:44 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
It is difficult from me to see how much of the pilot flame actually comes in contact with the metal plate opposing the electrode. There is only a small sight glass for viewing. I've considered trying to run my furnace with the burner cover removed, but I am nervous about doing this. I would have to bypass my pressure switches to run the furnace in this way.

My main burners never have trouble lighting, so I assume the pilot flame is registering properly. Does the pilot remain on while the main burners are on? I assumed it shuts off and the flame rectification then occurs from the main burner flame.
 
  #28  
Old 01-26-10, 04:48 PM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
You may not even have to bypass the pressure switch. But even if you do - no big deal.

Well, I came back to say......I can't speak for every mfg'er - and maybe how they design them. Of the closed combustion furnaces I have opened up - they ran. But by chance somehow that yours is designed in such a way that the indtroducion of room air would cause the flame to flash, or delay ignition - try running it with the pressure switch as is first, and report back if your furnace will run that way, with the burner cover removed.
 
  #29  
Old 01-26-10, 05:22 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Again I agree with Ecman. In my experience, the furnace will still operate if you remove the burner cover.

The pressure switch is sampling the opposite end of the heat exchanger, so opening the burner compartment doesn't affect the negative pressure that needs to develop to close the pressure switch.
 
  #30  
Old 01-28-10, 05:20 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I ran my furnace last night with the burner cover removed. SeatlePioneer was correct, my pressure switches still worked even when the cover was removed. This allowed me to clearly view the ignition/burner process.

During a heat call my pilot lights up immediately and I have a good sized flame that comes in direct contact with the grounding plate that opposes my ignitor electrode. The flame probably exceeds this grounding plate by about 1". Within a few seconds of my pilot lighting, the main burners ignite and it appears that the pilot flame shuts off. Within a minute or so of running the grounding plate that opposes my ignitor electrode becomes so hot it is glowing red. I again tested my flame retification and only measure about 0.1 uamps of current. Any other ideas that could improve my flame retification? Should I try running a direct ground lead to my pilot assembly?
 
  #31  
Old 01-28-10, 06:25 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by gmc1972
Should I try running a direct ground lead to my pilot assembly?


I would. In my experience the Honeywell pilot assembly usually has a wire running from one of the screws holding the pilot burner in place to a chassis ground. But I'd try running a wire from the pilot burner like that directly to the terminal on the ignition module to see if that improves the uamps, or simply connecting your multimeter in place to form that connection.
 
  #32  
Old 01-28-10, 10:58 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thanks, I will run this test this weekend and let you know how it works on Mon.
 
  #33  
Old 01-31-10, 05:06 AM
G
Member
Thread Starter
Join Date: Dec 2009
Location: Michigan
Posts: 18
Upvotes: 0
Received 0 Upvotes on 0 Posts
I tested my flame retification with my multimeter connected directly to my pilot assembly bracket and to my burner ground terminal on my ignition module. I still only measured about 0.1 uamps of current.

However, since cleaning my pilot assembly and ignitor electrode last week I haven't noticed any intermittent burner shutdowns. Only time will tell if this resolves my problem but so far so good.

So now I'm wondering if my multimeter is working properly or if I somehow did not test the flame retification correctly. Could the spec on my furnace flame retification be less than 3-5 uamps? Either way I'm happy it seems to be working now! Thank you SeattlePioneer and ecman51, I appreciate all your help!
 
 

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