I am back with a similar problem I faced about a year ago (wonder if it's going to be an annual event ). Last time I used to see code 33 followed by 13. The service confirmed a defective blower motor as folks here had indicated and replaced it. The problem went away.

Few days ago, Nest reported that the furnace was stopping frequently and I noticed code 33 again. Only this time there was no code 13 and it seemed to recover after 4 minutes. Here is what I see today -

- Furnace turns on
- After about 15 seconds, the blower turns on
- Both continue to run for 4 minutes
- Code 33 starts flashing and the furnace stops
- Blower continues to run for another 4 minutes and then stops
- The light becomes steady
- Another 10-15 seconds, the furnace turns on and continues with the above cycle

For code 33 (Limit or Flame Rollout switch is open), here is what I have done so far -

1. Defective blower motor or capacitor - there doesn't seem to be any issue with the blower this time. No noise while starting, no burning smell and seems to run smoothly
2. Dirty filter / restricted dirt system - I replaced the 20x20 filter even though it was replaced a month ago and wasn't dirty at all. Also, ensured all registers are open and flowing air when the blower runs. Didn't help. Wonder if I should run the system for 4 minutes without any filter and see if it still stops.
3. Loose blower wheel - there is absolutely no unusual noise when the blower runs so this seems unlikely
4. Defective switch or connection - This could be a problem. How do I verify this? I couldn't locate a red button inside the burner compartment
5. Inadequate combustion air supply (flame rollout switch or fuse link open) - Is there a way I could check this as well?
6. Open flame rollout switch or fuse link. Manual reset or replace - I'd like to replace and see if that helps (this seems to be the easiest and most economical option)

Seems like #4-6 are more likely. What would you have me try? Thanks for any guidance.

 

Do you have a meter? You need to see which switch is open.

 

I do - which switch should I start with? Here is the burner compartment -

 

I see one switch (set to ON) -


Or, are you talking about these?

 

No, you need to check the limit and rollout.

 

Are they in this picture? Let me google a bit.

 

I think this is the one? Checked this - shows closed (0.0 ohm) -


Wonder what this is but shows closed -

 

I tried resetting after turning power to the furnace off (pressing the red dot) and then turning the furnace off. The light started flashing code 33 again and after 4 minutes furnace and blower both started again and ran for 4 minutes.

If it's a switch, it precisely opens after 4 minutes and then closes after another 4. Shouldn't be heat related as I tried it this time with the burner compartment open so heat build-up should have taken longer than 4 minutes.

 

Anything else should I try folks?

 

http://www.doityourself.com/forum/ga...s-furnace.html

Read through the thread above. Your are both trying to identify a problem.

But make any reply on this thread so as not to sow confusion.

 

Thanks SeattlePioneer. Yes, the problem seems similar. I haven't tried running the furnace for more than 15-20 minutes (2-3 cycles of 4 minutes) at a time so never had to recycle power like Neil needs to after about 40 minutes.

I'll try running for 30+ minutes tonight after removing both the filters to see if it's really the air filters.

 

Reading from the other thread, I wonder if I am looking at the right manual. Model number from the burner door is 59SC2B080S211120 I am looking at this. Odd that the PDF itself doesn't list any model information. My installation is horizontal though.

 

Ran for about 90 minutes and it didn't need any power recycle. But it stopped every few minutes so it's not really a constant run like Neil's.

The continuous runtime wasn't constant - one time it ran for almost 6 minutes without stopping and other times between 4 and 5 minutes. I had removed both the filters so that might have to do with longer runtime but since it didn't eliminate the stop, can I now rule out that dirty filter or registers causing it?