Sears Furnace - inconsistent burner lighting

Reply

  #1  
Old 11-06-11, 06:12 AM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 4
Sears Furnace - inconsistent burner lighting

My Sears gas furnace is having a problem. The burners sometimes won't light. (Sears model: 867.769234, Ser#: H619 66779, MFR: SUGK100AH02)
It seems to happen most often first thing in the morning after it's been off all night because the setback temp hasn't called for it to be on. The blower comes on and runs and runs but the burner doesn't light.
I have no idea how old it is, but we moved into this house (2400 sf Cape Cod in Western NY) in 1990 and the furnace was already installed.
My brother is retired from the HVAC biz so of course I always call him to come and take a look when my furnace is busted. He came over, put a meter on it and said that he couldn't find anything wrong with it. He advised me to vacuum it out and to take my air compressor and blow out the inside of the burners and the combustion chamber, which I did. A fair amount of brown stuff came out, but after a while that stopped. I vacuumed everything I could vacuum including the area where the pilot lights the burners.

Still the problem persists. As I said, it seems to happen when the furnace starts after having been off for some time and I've noticed this problem most often in the early fall and late spring (when the furnace doesn't have to run as much).
In 2005, I replaced the gas valve and the pilot spark unit. I'm pretty sure those aren't the problem because the spark unit works (when it works) and the gas valve obviously opens when the burners do light.

Sorry this is so long....anybody have any ideas?
 
Sponsored Links
  #2  
Old 11-06-11, 07:04 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Take the cover off the burner compartment of the furnace and describe the sequence of events that occurs when the furnace lights up.

Post the make and model of the ignition control you replaced.

When the furnace fails to light up you need to be able to describe how far along in that ignition sequence the furnace is.

I presume your brother didn't observe the furnace when it was failing to light.
 
  #3  
Old 11-06-11, 08:34 AM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 4
Thanks for the reply.

You're right about my brother not observing the problem. It's like when you take your car to the mechanic and it won't exhibit the problem.

The ignition module is a Honeywell S8610U-1003.

I'll observe it tomorrow AM and report back.
 
  #4  
Old 11-07-11, 03:36 AM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 4
Well...I was sitting in the basement this AM waiting for the furnace to come on for the first time (sounds kinda weird doesn't it) and here's the sequence of events:
1. exhaust blower starts
2. spark module comes on
3. pilot light is lit
4. burners come on.

Of course...since I was sitting there watching it worked as it should.

I did notice that after the pilot flame lit the burners didn't light for ~ 10 seconds and during that time, even though the pilot flame was burning the spark module "sparked" briefly a couple of times.

I don't know if this tells you anything and I know that if I can't get it to exhibit the problem it's tough to help me.

Thanks in advance.
 
  #5  
Old 11-07-11, 06:38 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Usuallt the Honeywell S86XX module lights the pilot very fast, and is lightning quick about turning on the main burner gas once the pilot is lit.

The spark only shuts off if the module detects that the pilot is lit. Once that is detected the next step is to turn on the main burner gas.

I'd check to see when 24 VAC is being switched on at the gas valve. Probably the module is failing to turn on the voltage to open the gas valve, but it could be a sticky or failing valve that's not opening despite the voltage being turned on.

Polish the metal cage surrounding the pilot burner a bit to clean off any oxides that might be preventing the pilot from being detected.

I would say that the likelihood is that the ignition module is bad and needs to be replaced, but the tests above could identify a different problem.
 
  #6  
Old 11-08-11, 03:57 AM
Member
Thread Starter
Join Date: Nov 2011
Location: USA
Posts: 4
Same thing this AM. Burners lit with no problem whatsoever.

Difficult to diagnose if it won't misbehave.
 
  #7  
Old 11-08-11, 02:32 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Intermittent problems are the bane of repairmen.
 
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