Furnace burner won't re-light


  #1  
Old 11-26-08, 01:11 AM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
Furnace burner won't re-light

It seems this problem is common, but I'm not sure if the other threads match my issue exactly. We have a natural gas heater with a Honeywell ignitor using a spark ignition for the pilot.

The heater kicks on and pilot lights the burner as expected. As expected (I think) the burners cycle off after a couple minutes, and the blower stays blowing. After a short period, the ignition sequence begins again... spark, pilot lights, burners light, but only for a second, then goes out. (Sometimes the burners do not instantly light, but the pilot always lights.) This repeats, and repeats, and repeats, and the air coming out gets cold. One time while watching it, the burners lit and stayed lit, but normally, they just go out an instant after igniting. The Honeywell S86H clicks a lot during this. If I turn down the t-stat, wait for the blower to stop, and then turn the t-stat back up, the heater turns on and the burners burn as expected. The problem seems to be re-lighting after it cycles off.

The t-stat was replaced in the summer by the city (worked for A/C, but heater never tested until now). I don't know if the t-stat has anything to do with this problem. It's a White Rogers programable.

Any advice to troubleshoot/fix this will be appreciated, especially with Thanksgiving being around the corner.

Thanks!
 
  #2  
Old 11-26-08, 06:47 AM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Your problem is pretty typical.

Rule out t-stat by voltmeter testing for 24 vac at W terminal connection where stat wires are screwed onto a strip. Allow the furnace to run so that it goes out the way you are complaining of. Then test while this occurs. See if you lose the power there. If yes, bad stat or bad stat wire, or bad stat wire hookup to stat. If no - -

Then likely you have either have a partial clog at the burner end of the pilot where the orifice needs to be cleaned. Or a flame sensor there is dirty and needs to be cleaned. Or the flame sense to ground circuit needs cleaning up and to make sure the Honeywell and wire is grounded good. Or possibility pressure switch is shutting off, so be sure to volt check for 24 vac from each pressure switch terminal to ground to make sure that the incoming and outgoing wire still has 24 vac. Or the Honeywell module is bad, as a last resort, if all these checks out okay.
 
  #3  
Old 11-26-08, 08:55 AM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
This is the exact info I needed to start diagnosing. Thanks so much!
 
  #4  
Old 11-30-08, 10:19 PM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
Based on your ideas, I have throughly checked my system. The stat seems to be working fine. I re-grounded the Honeywell ignitor controller, checked all points for proper volts and checked wires. Everything seems to be in good electrical working order. I cleaned the ignitor/sensor. It is a Honeywell all in one sparker/sensor. Unfortunately the problem continues.

When the unit tries to restart, I can hear the Honeywell controller properly clicking, so I don't think it is the pressure valve. Despite the cleaning not working, I kinda feel like it is the ignitor/sensor. I cleaned it the best I could with steel wool. It operated a little different but ultimately the main burners would not stay lit for more than a couple seconds.

Is there a way to check the sensor part of the ignitor/sensor?

I may also try running a ground direct from the control to the pilot burner?? I came across an old manual suggesting this in case the metal structure of the furnace is an unreliable electrical conduit.

Thanks for all the help!
 

Last edited by Chilly in Texas; 11-30-08 at 10:49 PM.
  #5  
Old 12-01-08, 04:29 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
Can you see any sparking in the burner? You could try to disconnect the end in the burner, if in doubt, and try to spark it to a good metal ground out where you can see if it sparks. Then we can go from there.
 
  #6  
Old 12-01-08, 05:14 PM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yeah, it sparks, the pilot lights, the main burners light, and then quickly it all shuts down... after about one second of burning.
 
  #7  
Old 12-01-08, 09:40 PM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
I ran copper wire directly from the bracket holding the pilot sensor/ignitor straight to the ground on the honeywell controller. No change.

To recap... the furnace lights as expected when signaled by the stat. After a couple minutes the Honeywell Controller (S86H) clicks and turns the main burners off. The fan continues. After about 30 secs, the Honeywell controller clicks again the pilot lights (spark stops), main burners light, but only for a second or less. The Honeywell controller clicks and turns the burners off. It will continue to click and have these false starts with the burners. Sometimes it will catch and allow the burners to keep going, other times it will just keep clicking (and eventually blowing cold air). If I turn the stat down, let the fan stop, and then turn it back up. Everything repeats as above... the main burners burn for a couple minutes, etc...

I don't know what is normal in this cycle. I have checked everything out from the suggestions below. It seems to either be the sensor/ignitor or the Honeywell controller.

Any ideas/suggestions? Since the ignitor stops sparking when the pilot lights, can I rule out a problem with the flame sensor? (This model has the sparker and flame sensor all in one.)

Thanks again.
 
  #8  
Old 12-02-08, 07:59 AM
E
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 7,826
Upvotes: 0
Received 1 Upvote on 1 Post
Originally Posted by ecman51`
Then likely you have either have a partial clog at the burner end of the pilot where the orifice needs to be cleaned.
Have you looked into this.

Also make sure pressure switch not shutting down.
 
  #9  
Old 12-02-08, 08:59 AM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
I have... pilot is clean.

I rechecked the stat this morning, and to my surprise it was showing voltage drop at the W terminal during the shutoff/re-light attempts. I had checked this before, but must have missed it. I bypassed the stat and the heater worked fine, no cutoffs/re-lights.

Are the burners supposed to cycle on and off, or do they burn constant until the desired room air temp is achieved?
 
  #10  
Old 12-02-08, 12:31 PM
Jay11J's Avatar
Member
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 16,984
Upvotes: 0
Received 0 Upvotes on 0 Posts
What do you have for t-stat?

The burners, and power should be on all times for call of heat, and stops when the t-stat no longer calls for heat.
 
  #11  
Old 12-02-08, 12:52 PM
C
Member
Thread Starter
Join Date: Nov 2008
Posts: 9
Upvotes: 0
Received 0 Upvotes on 0 Posts
I have a White-Rogers programmable installed by the city electric company. (The kind they can shut off during peaks in the summer.)

The city came out today, and he believed that the problem is that the current setup does not have a 5th wire for a Common. (the stat is in power stealing mode) He said he has seen problems and irregularities with this stat working with gas furnaces in power stealing mode.

He suggested I either go buy a basic stat or run new wiring.

Does this make sense?
 
  #12  
Old 12-02-08, 01:07 PM
Jay11J's Avatar
Member
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 16,984
Upvotes: 0
Received 0 Upvotes on 0 Posts
Originally Posted by Chilly in Texas
I have a White-Rogers programmable installed by the city electric company. (The kind they can shut off during peaks in the summer.)
What kind of break are they giving you on this?

Lot of tech HATE them.. They are hard on your equipment, and I got rid of mine.. Our power company only gave us $3 a month credit.. Was not worth it for me, and my comfort that I lost with it.


Does this make sense?
Oh yes! that's why I was asking to see what you got, power stealing stat screws up a few furnace here and there.

If the City is giving you good credit, and you had no issues last summer keeping up with cooling, then run the 5th wire, but if you had a hard time keeping temp, and credit is worthless, then get rid of it, and get a Honeywell T-stat. They run on battery if you are not able to pull new wire.
 
 

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