Gas Furnace Lighting Issue


  #1  
Old 11-30-08, 10:29 AM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
Gas Furnace Lighting Issue

Good afternoon.

I have a gas furnace that is roughly ten years old. It has recently developed an issue upon starting. When I hear the thermostat call for heat, I hear the unit "click" for the spark. I then hear the flames start. Then everything goes quiet. Then I hear the unit "click" for the spark, flames start, quiet.

I opened the unit, removed the flame sensor, and cleaned the rod. I used a dollar bill, the unit appears clean, and is not scratched.

I re-assembled the unit, then I watched the unit with the front open. There is spark, flame, flame goes out, then I hear the gas valve open for a fraction of a second, then quite.

This process cycles about six times until the unit fires, then it works fine. Nice blue flames.

The unit is a Comfortmaker. The spark control is a Honeywell S8600M.

I hate to continue using the unit "cycling" like that because I am sure that it will lead to further problems. Any advice is greatly appreciated.

Steve
 
  #2  
Old 11-30-08, 12:08 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
Direct spark to burner? Or, spark to a pilot light? How many burners?
 
  #3  
Old 11-30-08, 12:46 PM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
The spark lights a pilot. There are four burners.
 
  #4  
Old 11-30-08, 02:17 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Flame sensor

I presume you cleaned the flame sensor on the opposite end from the pilot. If I remember correctly, the pilot assembly also has some sort of flame sensor. I suggest removing & cleaning the entire pilot assembly.
 
  #5  
Old 11-30-08, 04:03 PM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
I had removed the entire flame sensor/pilot assembly from the burner. I then removed the flame sensor (the piece with the wire attached?) from the assembly, and cleaned it real well. (I used a dollar bill to wipe the piece)

The other pieces of the assembly seemed to be made of steel. I tried to clean them some, but I did not clean them with steel wool or sandpaper. They felt rough to the touch. (as compared to the piece with the wire attached)

Should I clean these pieces better, maybe with some steel wool?
 
  #6  
Old 11-30-08, 04:15 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Flame Sensor

If the pilot assembly is near one end of the row of burners, check the opposite end for another flame sensor. Make sure the connection from the sensor to the control is clean & tight.
Make & model of the furnace might help as well as the make & model of the igniton control.
 
  #7  
Old 11-30-08, 07:22 PM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
Here is more information on the furnace.

Comfortmaker. The label inside says ICP.

Model # FBF100F20A2
MFG. # NTG3100KFA2
Model # NTG3100KFA2

The spark control is a Honeywell #S8600M

The flame sensor/pilot assembly is in the center of the burners. I did not see any other flame sensor. There is only one wire coming from the assembly, and it goes to the spark control, and plugs onto the "spark" terminal.
 
  #8  
Old 12-01-08, 05:18 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Center Pilot

Clean the flame sensor with a Scotch Brite pad or steel wool you've washed in alcohol to remove any oils. You can use a small wire brush on the rest of the pilot assembly. Blow out the pilot tube with canned or compressed air. The tube MUST NOT be connected to the gas valve when you blow it out.
 
  #9  
Old 12-01-08, 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
I reread his OP, since now it is clear beyond all doubt that he has a pilot system. It also has symptoms of a partially clogged pilot orifice that does not allow enough pilot flame to be sensed. I have had a couple of these in not too distant past, that fixed the problem.
 
  #10  
Old 12-01-08, 08:44 PM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
I'll give the scotchbrite and alcohol a try. I'll also clean the pilot tube/orifice.

Thank you for the advice, and I'll let you know how it goes.
 
  #11  
Old 12-02-08, 06:18 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Alcohol

You don't need to wash the ScotchBrite with alcohol. Only if you are using steel wool do you need the alcohol. The alcohol is only to remove oils used in the manufacture & for rust prevention of the steel wool.
 
  #12  
Old 01-02-09, 12:00 PM
S
Member
Thread Starter
Join Date: Nov 2008
Location: Atlanta, Georgia
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
Hi guys,

I hope that everyone had a great holiday season.

I tried the scotchbrite on the flame sensor. I thought that it had worked, but now I am back to the same problem. Spark, flame, flame goes out. Repeat (several times) then the furnace will light and stay lit.

Steve
 
  #13  
Old 01-02-09, 05:37 PM
Grady's Avatar
Forum Topic Moderator
Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Received 41 Upvotes on 39 Posts
Pilot Flame

If you can get a picture of the pilot flame & post it, we might be able to see something. I'm leaning toward Ecman51's idea of a partially clogged pilot orifice.
 
  #14  
Old 01-02-09, 07:23 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
Sequence of Operation of Honeywell Intermittent Pilot

With the Honeywell S8600 ignition module, the spark and gas for the pilot light should turn on and the pilot light should light. The presence of the pilot flame is verified very fast by flame rectification and the spark shuts off. At the same time the main burner gas should turn on and light off the pilot light, and stay on until the thermostat is satisfied.

The sequence of operation appears to be normal until the main burner is switched on, at which point the main burner fails and shuts off, causing the ignition cycle to begin again.

This suggests that the gas supply is failing when the main burner turns on.

One thing to look for would be to examine whether the pilot lights fails at the same time as the main burner, which would support the theory of a shortage of gas supply.

Another thing to test would be to pull the wires off the MV connection on the gas valve, to prevent the main burner gas from turning on. Let just the pilot light burn for a bit and check to see if that is stable, or whether the pilot light gets smaller because of a diminishing gas supply.

Is this a natural gas furnace or propane? Are the weather conditions unusually cold? Check all the gas valves going to the furnace to see if any may be partially closed --- going back to the gas meter or propane tank.

Do you have any other gas appliances? Are they operating normally?

If I were doing this I'd be measuring the gas pressure just before the furnace gas valve to see if that's dropping when it should not. There are other ways of testing that, but I'd be interested in seeing the results of some of these checks before going further.
 
 

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