Lennox G50DF(x) wont ignite all the time.

Reply

  #1  
Old 11-13-12, 06:49 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
Lennox G50DF(x) wont ignite all the time.

My furnace won't heat continually. The fan turns on, and the burners will turn on for only a couple seconds, then shut off. This will happen 4 times, and then stop completely. The indicator lights are "alternating slow" flashing. The manual says it's in "watchguard", but the manual gives no help on how to fix it. Is this a doityourself fix, or do I need to call someone?

I found this above paragraph on a post and this is what mine is doing. BUT, I have tried to clean the ignitor and the other Flame sensor on the opposite side and had no luck in fixing it.
It seems to work for a little bit and by a little bit im mean, sometimes its a day, sometimes its for a few hours. I live in ohio and its starting to get cold and i have a little one in the house now. Should I buy a new ignitor and Flame sensor? Do you think they are still my problem?

thank you
kevin

 
Sponsored Links
  #2  
Old 11-13-12, 10:23 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Check carefully to be sure that your ignition control/circuit board are well grounded to the furnace sheet metal. It might be worthwhile to polish those electrical connections or to screw in connections to the sheet metal again. Check the wires from the flame sensor to the circuit board for any wear or deterioration.

Is the flame sensor engulfed by the burner flame when the burner turns on?

Do you have a multimeter and understand how to use it? Does your multimeter read down to one microamp (1,000,000 amp)?
 
  #3  
Old 11-13-12, 10:34 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
ok, I will look at the control board this evening and make sure it is grounded good. and I'll inspect the flame sensor connections and wire.

The flame sense seems to be engulfed in flame when it does light.

I do have a multimeter. I will have to check to see if it goes down to one microamp.

I will do this tonight and report back tomorrow morning.
 
  #4  
Old 11-14-12, 06:01 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
I made sure the control board was grounded good.
I re-cleaned igniter with sand paper.

The furnace worked for a couple hours then went back to the Slow Alternating Flashing lights and it wouldn't ignite or if it did ignite it wouldn't stay lit.

I do have a mulitmeter. is there something else i can check.

I took a picture of my control board. is has two things on the front that the diagrams dont show. im not sure what they are.

Name:  IMG_5251.jpg
Views: 8231
Size:  50.9 KBName:  IMG_5252.jpg
Views: 1570
Size:  34.7 KB
 
  #5  
Old 11-14-12, 09:10 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Usually there is a list of diagnostic codes posted on the furnace. What is the explanation for the code your observe --- the alternating flash?


Measure the AC voltage being applied to the flame sensor when the furnace is going through the ignition process but fails to light. Usually that voltage will be 24 VAC, sometimes 120 VAC.

You might find a reduced or zero voltage if the ignition module is failing to turn on the correct voltage.

You want to measure that voltage from a connection on the flame sensor to the furnace sheet metal ground or the C terminal on the circuit board.
 
  #6  
Old 11-14-12, 09:20 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
The indicator lights are "alternating slow" flashing. The manual says it's in "watchguard", but the manual gives no help on how to fix it.

You might find a reduced or zero voltage if the ignition module is failing to turn on the correct voltage.

if this fails then do i need to by a new igniter?

thank you



 
  #7  
Old 11-14-12, 11:44 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
The igniter doesn't seem to be the issue. From your description it lights the gas, which is it's only function.

The flame sensor circuits checks to determine if the gas has been lit once the gas valve is turned on. If the flame sensor circuit of the circuit board doesn't detect that the gas has been lit within three seconds or so, it shuts off the gas and attempt to light the gas again a few times.

Failure to verify that the gas lights will cause the burners to shut off and the diagnostic code you are getting to be switched on. So there is no reason to suppose that a new ignitor will do any good.

What you need to do is to test the flame sensor circuit to see if it is defective. If it is, you will need a new circuit board. Checking for that voltage on the flame sensor is a good place to start.
 
  #8  
Old 11-16-12, 07:08 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
I tested everything and it all seemed good.

After further inspection and digging around and some help from my dad. It turns out the lid on my chimney on the roof broke and almost closed up the chimney. So the pressure switch was shutting things down. Propped up the chimney lid and everything is working. Going to fix the lid this weekend.

thank you for all your help.

kevin
 
  #9  
Old 11-19-12, 06:06 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
WELL, I thought i had it fixed. Propping up the chimney worked for about 2 days. so im not sure what the heck is going on.

I thinking about just buying a new control board and a new flame sensor.

I tried to by pass the pressure switch but it wouldn't let me do that so see if that was the issue. I was thinking maybe i had something clogged in the chimney.

You want to measure that voltage from a connection on the flame sensor to the furnace sheet metal ground or the C terminal on the circuit board.

I measured this. I got 6 volts. So does this sound like i need a new control board? I thought it seemed weird that once i gave the chimney more air to breathe that it worked for a couple days.

thanks for the help


 
  #10  
Old 11-19-12, 07:11 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
<< I thought it seemed weird that once i gave the chimney more air to breathe that it worked for a couple days.
>>


Repairing a venting issue is always worth doing. We are still diagnosing the issue you reported, which so far anyway doesn't seem to be a venting issue, but an issue of detecting the burner flame.


The next step would be to put your meter in series with the flame sensor and measure the DC microamps when the furnace is lighting. A microamp is 1/1,000,000 amp, so you need a sensitive meter for this because you need to measure down to one microamp or even less.

Let us know what reading you get when the flame sensor is actually engulfed by the burner flame.
 
  #11  
Old 11-19-12, 08:19 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
ok I will try that. but only if it ignites. Last night it would ignite for one second and shut down. then the igniter would heat up a few more times and i would hear a couple clicks each time but no flame at all.


so does the 6 volt measurement not mean anything?

you said to do this:
Measure the AC voltage being applied to the flame sensor when the furnace is going through the ignition process but fails to light. Usually that voltage will be 24 VAC, sometimes 120 VAC.

You might find a reduced or zero voltage if the ignition module is failing to turn on the correct voltage.

You want to measure that voltage from a connection on the flame sensor to the furnace sheet metal ground or the C terminal on the circuit board.

 
  #12  
Old 11-19-12, 10:12 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
I would have expected you to find 24 VAC. That suggests that the circuit board is bad. Measuring the microivolts will help to confirm that.


Your furnace manual is at:

http://www.lennox.com/pdfs/installat..._G50DF_IOM.pdf


I'd print that out and keep a copy at your furnace.


What should be happening:


The hot surface ignitor should heat up for 20 seconds

The electric gas valve should turn on the gas for four seconds and the ignitor should remain energized for four seconds.

The burners should light off the HSI and you should have four seconds to be able to measure the flame rectification current.

It sounds like the ignition procedure described above is stopping too early, is that right?

Is the gas being turned on by the electric gas valve?


That suggests a defective ignition control that needs to be replaced.
 
  #13  
Old 11-21-12, 07:15 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
looks like my board is ok.

looks like my problem is the Gas Control Valve. new one is on the way.
thank you for your help
 
  #14  
Old 11-21-12, 08:42 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Received 0 Votes on 0 Posts
Actually, I recommend against DIY gas valve replacement since the correct gas input to the furnace needs to be set when a gas valve is replaced.
 
  #15  
Old 11-21-12, 11:06 AM
Member
Thread Starter
Join Date: Nov 2012
Location: United States
Posts: 9
Received 0 Votes on 0 Posts
hmmmmmm ok. thank you. I'll call a professional.
 
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: