Trane XV80 Intermitent Ignition Problem

I am having an intermitent problem with my Trane XV80 furnace failing to ignite periodically over the last week. System is 20 years old and has run fine with no maintenance problems for the 8 winters we have owned the home. Last week, I started noticing that sometimes when the thermostat is calling for heat, the furnace just blows cold air. Furnace diagnostic LED is 2 flashes = "system lockout (no flame)".

First time this happened, I changed the filter. Turned system on and it worked OK.

Next time it happened, I cut power to system, then restored power and it worked OK.

Last night, it happened again. Powered down to reset, but upon restart it would not ignite. I pulled the cover and observed the following sequence: draft blower is energized, ignitor glows, no flame. This is repeated 2 more times until the system locks out and the blower turns on blowing cold air. Tried resetting again, but it would not ignite. I left the system off all night and house got down to 53 degrees by this morning, at which time I restored power and it ignited fine and ran for several hours until thermostat was satisfied at 66 degrees.

Any advice on what diagonostic steps I need to take to determine the source of the problem? It appears that the system will ignite most times, but not every time, it is called.

 

Clean the flame sensor (annual maintenance) and then report back if it works. Do the burners light every time? Or do they light and then go out.

 

I just cleaned the flame sensor with steel wool... we'll see how things go tonight and tomorrow.

 

OK, here's what has happened since I cleaned the flame sensor:
I have the thermostat set to 64 degrees at night, 66 degrees during the day.

This morning when I got up, the thermostat was at 66 degrees, but the house was at 60 degrees. The furnace was on and heating. It stayed on until the thermostat was satisfied at 66 degrees. Not sure what happened for the house to get down to 60 degrees last night. It implies that the furnace had trouble igniting (or possibly ignited and then went out), but then was able to try again and ignite successfully at some point.

When we returned from church just now, the thermostat was at 66 degrees and the house was at 64 degrees. Again, the furnace was on and heating. So, similar situation to this morning.

There's no way for me to tell if the burners are lighting and then going out unless I witness it, right? So far, I have not seen this happen, but it could be happening. Please advise on next diagnostic step.

 

you will have to be able to verify the burners are out and catch the diag code. Hopefully you will be able to duplicate the problem as well. When it is acting up you need to write down the sequence of events in order that do happen with a call for heat but a failed ignition. You may have to cycle the thermostat a number of times to get it to happen. Intermittent problems can be very hard to diagnose.

 

I just caught the furnace with the blower on and no heat. Same code as before - 2 flashes = "system lockout (no flame)". I disconnected power to unit then back on, and this initiated the ignition sequence. As I mentioned before, the system will make 3 attempts to ignite before giving up. Here's what I saw: no flame on the first 2 attempts, but it did ignite on the 3rd attempt. Here is the sequence I observed on the unsuccessful attempts: draft blower on, igniter glows for several seconds, gas jets on (I can hear the hiss), no flame. After the gas jets start, the igniter stays glowing for only a brief time (maybe a second or less) before the glow starts to fade. On the successful attempt, I noticed that the gas ignited right away once the jets turned on.

So, it seems that all the steps are occurring but the gas is just not igniting sometimes. Why? Is the igniter faulty (not getting hot enough)? Is the system sensitive to the igniter being in just the right spot? If so, maybe I need to adjust it? It is not directly in the path of the jet, but I assume that is by design.

 

The HSI may be getting weak, but first thing I would try is to remove the burners and clean the faces and crossovers.

 

 

OK, I removed all the burners and cleaned them. There was some surface corrosion. Not sure how much corrosion is needed to cause a problem. Tested system again, but no dice.

Then, I saw the diagram you sent and determined that the igniter was probably too far from the center of the burner. The igniter is mounted by a screw tapped into an aluminum angle, and allows for some adjustment, although there is a raised edge on the igniter whose purpose I assume is to maintain the correct alignment with the mounting angle. Anyway, I was able to move it perhaps 1/4" closer to the burner axis. Tested system again and ignited on the 1st try!

This seems promising, but I'll wait to see what happens in the morning to confirm all is fixed. I think the latest problem was the position of the igniter. But, I think I may have moved it out of position while messing with the furnace this weekend. I suppose the initial problem may have been a dirty flame sensor, or dirty burners. Hard to know at this point, but I don't really care so long as it is working.

 

Up to temperature this morning. All seems to be working correctly.

Thanks much for the advice!