Gas furnace locks out within a few hours

Reply

  #1  
Old 01-22-07, 08:14 PM
C
Member
Thread Starter
Join Date: Jan 2007
Posts: 5
Received 0 Votes on 0 Posts
Gas furnace locks out within a few hours

I have a Carrier 48SS-036100331-- (about 11 years old) and my house is
approx 1750sq ft. The heat works fine when the outside temp. isn't too cold
(ex. greater than 50 degreesF). However, when it is colder outside, the unit
frequently locks out (or perhaps it just locks out faster, or is just more noticeable). The exhaust fan continues to run, but the burner isn't
lit. It won't re-light until I flip the breaker off/on. I had to have my heat exchanger replaced last season. I vaguely
remember the technician saying it was likely there wasn't enough airflow, so
the exchanger was getting too hot which decreased it's lifespan. This made
me suspect that the limit switch was tripping. However, the led on the
controller board blinks 8 times when it's locked out, which corresponds to
"internal control fault" according to the schematic. I have opened all my
dampers to maximize airflow. When I flip the breaker off then on again to
the unit, the burner will light up again and will work for awhile (usually getting to the set temp) and then
lockout again (anywhere from 30 mins to 10 hours later). Here are pictures:

http://www.commercialinstallations.com/Misc/heat.htm

I cleaned the flame sensor and ignitor with steel wool and a wire brush on the ignitor so that it makes good electrical contact with the mount, but still locking out.

A couple of resistors on the control board look like they have been overheated. Not sure if that may be causing the problem though.

Any ideas? "Internal control fault" sounds like the controller board, but
why does it work for awhile after resetting? And why does it seem to lockout sooner when cold? What is the best way to
troubleshoot "internal control fault" error?
 
Sponsored Links
  #2  
Old 01-23-07, 05:26 AM
Jay11J's Avatar
Member
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 18,427
Received 0 Votes on 0 Posts
From what I can see it looks like it's ok.

The orange wire you got is the spark ignitor.. The flame sensor is the green wire. Have you cleaned that?

On the flame roll out, is there a reset button on that?

Only two things I am thinking is the flame sensor, or flame roll out.
 
  #3  
Old 01-24-07, 05:14 AM
C
Member
Thread Starter
Join Date: Jan 2007
Posts: 5
Received 0 Votes on 0 Posts
Thanks for the reply.

Yes, I cleaned both the flame sensor and the spark ignitor. I didn't see any reset button on the flame rollout.

It is weird, because it will work for several hours, but then it just locks out. Usually on the second (or perhaps third) call for heat.
 
  #4  
Old 01-24-07, 10:07 AM
P
Member
Join Date: Jun 2003
Location: CANADA
Posts: 109
Received 0 Votes on 0 Posts
Smile

I have the same issues you are talking about.Will work perfectly when outside temperature is above freezing point but will lock-up in real cold temp.Mine is a Coleman D.E.S 80 with hot surface ignition system (15 YEAR OLD).Had a tech replace the ignitor and module 2 year ago but now I'm having similar symptoms.Flue fan turns on, ignitor glows,gas valve opens(SOMETIMES) and will retry igniton 3 more times,unit goes into lock- up mode.In some cases if I'm lucky, the flame will ignite but will cut-off soon after.This happens mostly at night and when I wake up in the morning the house will be cold.I'm lucky I have a heat pump that will supply a bit of heat when needed.Last week I decided to clean the H.S.I with emery cloth and that did the trick for another 2 days making me think the H.S.I. is bad.I'm replacing the H.S.I today even if it looks good and will let you know what happens.According to what I've read on the net, these units works as a whole and if something goes wrong it affect the whole system.
 
  #5  
Old 01-24-07, 12:14 PM
J
Member
Join Date: Oct 2005
Location: USA
Posts: 1,076
Received 0 Votes on 0 Posts
If everything else looks OK, then it's time to suspect the circuit board.
 
  #6  
Old 01-24-07, 02:21 PM
P
Member
Join Date: Jun 2003
Location: CANADA
Posts: 109
Received 0 Votes on 0 Posts
The new ignitor didn't do the trick...I hear a faint click when the gas valve tries to open but so far no go.How do you test the ignition module? There should be a way since they cost $ 250 on my furnace.How can you tell its bad? Mine has no external sings of damage.
 
  #7  
Old 01-24-07, 03:05 PM
C
Member
Thread Starter
Join Date: Jan 2007
Posts: 5
Received 0 Votes on 0 Posts
Originally Posted by jim-connor View Post
If everything else looks OK, then it's time to suspect the circuit board.
Yeah, I'm definitely suspecting the circuit board, I just want to make sure I can eliminate everything else. Intermittent problems are the worst. When I sit out there and watch it, it runs fine. Yet, I wake up in the morning freezing because it goes out at some point during the night.

I'm planning on taking the circuit board out this weekend, checking a few components on the board, then reinstall, ensuring everything is well grounded and connections are snug. If that doesn't fix it, then I plan on replacing the board if I can find one.
 
  #8  
Old 01-25-07, 11:52 AM
J
Member
Join Date: Oct 2005
Location: USA
Posts: 1,076
Received 0 Votes on 0 Posts
There is really no way to field test the board other than direct substitution. We usually don't do that until everything else has been checked and no solution found.
For those who have a background in electronics, the usual failure of these boards are bad capacitors or relays.
 
  #9  
Old 01-25-07, 12:56 PM
N
Member
Join Date: Jun 2006
Posts: 125
Received 0 Votes on 0 Posts
next time the system cuts out, dont reset it, instead take a meter and check every safety switch: rollout, psi switch, limit and so on to see if you can find out what is opening causing the lockout. also check your air returns and supplys as well as your fan motor, its possible that the motor could be cutting out on internal overload, causing the limit to open, then the motor cools and starts back up when you reset power.
 
  #10  
Old 01-27-07, 08:16 PM
C
Member
Thread Starter
Join Date: Jan 2007
Posts: 5
Received 0 Votes on 0 Posts
I opened up the unit today and noticed two things of concern...

First, the contacts on the back of the limit switch had been bent so that they were touching, shorting the switch and defeating it's intended purpose! Surely the technician that replaced my heat exchanger last year would have noticed that. I wonder if someone did that intentionally at some point. Anyway, I don't know if that contributed to this problem somehow or not (perhaps overheating since the limit switch was shorted). I bent them away, so they were no longer touching. After un-shorting the limit switch, the heat still worked, so I think the limit switch is fine. We'll see tomorrow morning if it locks out again.

Second, the foil-faced insulation on the top and sides of the heat exchanger chamber has clearly been scorched by the heat exchanger in some spots and it is sagging from the top and on the walls. The top is sagging to the point that it is touching the top of the heat exchanger, which obviously can't be good. Any recommendations for adhesives I can use to get the insulation to stay on the top panel and walls? I doubt liquid nails or gorilla glue are designed to hold up under those temperatures.
 
  #11  
Old 01-26-08, 03:04 AM
Join Date: Jan 2008
Posts: 1
Received 0 Votes on 0 Posts
I have the same problem

Originally Posted by clsmith6 View Post
I have a Carrier 48SS-036100331-- (about 11 years old) and my house is
approx 1750sq ft. The heat works fine when the outside temp. isn't too cold
(ex. greater than 50 degreesF). However, when it is colder outside, the unit
frequently locks out (or perhaps it just locks out faster, or is just more noticeable). The exhaust fan continues to run, but the burner isn't
lit. It won't re-light until I flip the breaker off/on. I had to have my heat exchanger replaced last season. I vaguely
remember the technician saying it was likely there wasn't enough airflow, so
the exchanger was getting too hot which decreased it's lifespan. This made
me suspect that the limit switch was tripping. However, the led on the
controller board blinks 8 times when it's locked out, which corresponds to
"internal control fault" according to the schematic. I have opened all my
dampers to maximize airflow. When I flip the breaker off then on again to
the unit, the burner will light up again and will work for awhile (usually getting to the set temp) and then
lockout again (anywhere from 30 mins to 10 hours later). Here are pictures:

http://www.commercialinstallations.com/Misc/heat.htm

I cleaned the flame sensor and ignitor with steel wool and a wire brush on the ignitor so that it makes good electrical contact with the mount, but still locking out.

A couple of resistors on the control board look like they have been overheated. Not sure if that may be causing the problem though.

Any ideas? "Internal control fault" sounds like the controller board, but
why does it work for awhile after resetting? And why does it seem to lockout sooner when cold? What is the best way to
troubleshoot "internal control fault" error?
What ended up being the solution to the problem? If you could reply it would be awesome
 
  #12  
Old 02-17-08, 09:16 PM
C
Member
Thread Starter
Join Date: Jan 2007
Posts: 5
Received 0 Votes on 0 Posts
I ended up replacing the board and it has worked flawlessly since.
 
  #13  
Old 05-30-09, 08:38 AM
G
Member
Join Date: May 2009
Posts: 1
Received 0 Votes on 0 Posts
I had a similar problem and hope this information helps

Here is how I fixed the problem. --John

Symptom:

Intermittent furnace lockout with Internal Control Fault (8 flashes), sometimes accompanied by the "modified fan blower delay" fault (1 flash). Problem occurs especially when the temperature falls below 32 degrees. Checked rollout switches and flame sensors, no problem.

Cause:

Excessive vibration triggering the relays on the Integrated Control Panel, which cause the internal control fault (usually the vibration can be felt by touch on any part of the unit)

Temporary Fix:

Dampen the vibration to the control panel using high-temp flame-resistant padding. Alternatively, brace Integrated Control Panel compartment to something solid to dampen unit vibration.

Permanent Fix:

Vibration most likely due to imbalanced blower wheel (cage wheel inside the blower that pushes flame exhaust out of the unit). Replace blower wheel.
 
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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: