Hot surface Ignitor Problem

Reply

  #1  
Old 02-05-03, 06:45 AM
MikeMo
Visiting Guest
Posts: n/a
Hot surface Ignitor Problem

Hello,

I've done a lot of reading, and I've had my furnace open, so here's what I know.

My furnace is a Trane. I think it's an XL80. (I found an XL80 brochure, but the furnace itself doesn't say the model anywhere)

The ignition system is a White Rodgers 50E47-060 Hot surface Igniter. From what I understand, this system has 3 main parts:

1. Computer
2. Hot Surface Igniter
3. Flame sensor (I think)

When the thermostat calls for heat here's what happens on a good day:

A fan turns on (but not the blower yet). The hot surface heats up for 17 seconds until it is bright hot. The gas kicks on and the furnace ignites. The hot surface igniter shuts down. When the furnace is good and hot, the blower turns on and heats my home. I smile.

Recently, here's what happens:

A fan turns on (but not the blower yet). The hot surface heats up for 17 seconds until it is bright hot. The gas kicks on and the hot surface burns the puff of gas, but the furnace doesn't ignite. The gass shuts off. The hot surface shuts off. The hot suface turns on again(17 seconds). The gas kicks on and the hot surface burns the puff of gas, but the furnace doesn't ignite.....it does this 5-10 times. Then it stops trying. The computer has a little red light that blinks. The fan continues to run until I cut the power. If I wait 5 minutes and turn the power on again, it will try all over. Sometimes it ignites on it's 3rd or 4th try in the cycle.

In the above description, I'm not sure if the gas shuts off before the hot surface or vise-versa.

I have taken the furnace apart, just as deep as the hot surface ignitor and flame sensor. My furnace has 2 "torches". They heat 2 "drums" that are side by side. In front of one torch is the hot suface ignitor. It extends slightly into the first "drum". In front of the other torch is the flame sensor. It extends into the second drum. However, it seems to be mounted in a place that it is almost touching the inside wall of the drum.

I used a toothbrush on the flame sensor, (though it really wasn't dirty) and then I put some pressure on it to bend it slightly away from the wall of the "drum". Now the furnace ignites every time. In 3 or 4 days the whole thing will start up again, and I'll do my pushing trick again (because the sensor tends to drift back to it's original spot), and it will work again. Could it be the sensor needs to be replaced? Or perhaps just re-mounted more to the center of the "drum". The sensor looks like a pair of long skinny metal rods, one slightly smaller than the other. I just had the whole thing cleaned & serviced 2 seasons ago.

Any help is appreciated!

Mike Mo.
 
Sponsored Links
  #2  
Old 02-05-03, 07:32 AM
bigjohn
Visiting Guest
Posts: n/a
Good job of troubleshooting. Try a new sensor and see if that doesn't cure it.
 
  #3  
Old 02-05-03, 11:32 AM
MikeMo
Visiting Guest
Posts: n/a
more reading...

Since posting, I found in this forum many posts of the same thing---sorry for the repost. It sounds like the toothbrush had a big impact. But it makes me wonder....

If the hot surface is in drum 1 and the flame sensor is in drum 2, the furnace would have to ignite on torch 1 and then torch 1 would light torch 2 before the flame sensor would trigger----that means that the flame sensor position COULD have something to do with it. Remember I said it was kind of touching the wall of the drum? It is touching the COMMON wall. It may get the trigger from just a little rollout from drum 1. Drum 2 (with the sensor) may not even be getting lit!

Do you think that's possible?

Should I try to remount the flame sensor as far away from drum 1 as possible, while still keeping it fully within drum 2?

In my sketch below, the only difference is the position on the sensor. The perspective is looking into the drums, your eyes are the torches!

; is the flame sensor
= is the hot surface ignitor
() is a torch
Current position:

______________
[.........][.........]
[.........][.........]
[........;][.=......]
[....()...][...()...]
[______][______]

My idea:

______________
[.........][.........]
[.........][.........]
[.....;...][.=......]
[....()...][...()...]
[______][______]
 

Last edited by MikeMo; 02-05-03 at 11:53 AM.
  #4  
Old 02-05-03, 12:35 PM
bigjohn
Visiting Guest
Posts: n/a
How old is the furnace?
 
  #5  
Old 02-05-03, 12:37 PM
MikeMo
Visiting Guest
Posts: n/a
5 to 8 years old.
 
  #6  
Old 02-05-03, 01:51 PM
bigjohn
Visiting Guest
Posts: n/a
Is this a new problem or has it always done this?
 
  #7  
Old 02-05-03, 02:51 PM
MikeMo
Visiting Guest
Posts: n/a
Well, I've been in the house for 5 years, and it did it two years ago. So I had it cleaned, and they replaced the flame sensor. At the time, I had never even attempted to open the furnace.

Now it does it again. It makes me wonder if the sensor wasn't really bad the first time, just broken in. Perhaps it just needed to be repositioned so that it doesn't trigger prematurely from torch #1. But the installer used the same mounting holes as before, so now this one is broken in, and the same thing happens.

Although, maybe I think I know more than I really do...it;s the engineer in me...

Mike
 
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: