PAYNE, PG8UAA, FURNACE, Blower running

[sbdivemaster]

Started having a problem last week where there tstat would reach temperature with the heater on, then tstat would quickly click twice and blower would keep running. I unplugged the furnace, took the Chronotherm III tstat off the wall, plugged the furnace back in and the blower keeps running. I figured the tstat was shot. Got a new Honeywell Pro4000 tstat, wired it up, plugged the furnace back in, and the blower keeps running.

Finally, I realized there is a blinking LED that gives out a code. The code is "33" (three fast blinks, 3 slow blinks). According to the service label:

33 - LIMIT OR FLAME ROLL-OUT SWITCH IS OPEN - If open for longer than 3 minutes, code changes to #13. Check for:

-Blower motor failure

-Motor start capacitor

-Open flame rollout switch, manual reset

-Inadequate combustion air supply (flame rollout switch only)

-Dirty filter

-Defective limit switch or connections

-Loose blower wheel

OK, I know nothing about HVAC, but I can learn. I'm thinking that I can eliminate the following:

-Blower motor failure: No, blower is running

-Motor start capacitor: Blower is running, but I don't know about this one.

-Dirty filter: No, filter is clean

-Loose blower wheel: Not sure, but don't hear any abnormal sounds

So, unless I am mistaken on the previous, that leaves

-Open flame rollout switch, manual reset. Is this something I reset? If so, how?

-Inadequate combustion air supply. I find this unlikely, as the furnace worked fine 8-10 hours prior, and was off while we were asleep. But I have been wrong in the past...

-Defective limit switch or connections. How do I test for this? If this is the cause, can I replace it?

I can provide more info upon request, as well as provide pictures of anything if needed. Also, I can hook up the old Chronotherm III tstat if needed to assist in troubleshooting.

This 14 year old unit blows both our heat and our AC. We're right at the end of furnace season, and it should be a couple of months before we really need AC, so this isn't a bad time to work on this. We just aren't in a position to replace the unit at this time, so I am hoping I can fix it to keep it running for a few more years while we save up for a replacement.

What do the resident HVAC gurus think?

Thanks in advance for any help.

[sbdivemaster]

PROBLEM SOLVED

First, I thought I would go back to where I started; I took down the Pro4000 tstat and replaced the Chronotherm III. Well, the Chronotherm is dead. It was fine when I took it off the wall last week. The screen is blank. I replaced the batteries. Nada. I checked the batteries, cleaned up the contacts on the tstat. Nada. It's dead. Now, I'm glad I did order the Pro4000.

So, I put the Pro4000 back on the wall, hook it up, plug the furnace back in and the blower is running... grrr. Unplugged it.

I searched around online, and found some tips on the "33" code. I opened up the furnace, reached my hand back in there and tapped on the limit switch. Put the furnace back together, plugged it back in. No blower. I went and raised the temp at the tstat. Woosh! The flames fired up, blower turned on, and heat came out of the registers! Switched it to AC, lowered the temp at the tstat... Voila! AC turned on, blower turned on,and cold came out of the registers. Everything works fine now with the new tstat.

If you have a Payne PG8UAA (or similar model with the same kind of limit switch), locate the limit switch and tap on it with your finger.

Give that a try before calling out the service tech.

Now, back to my regularly scheduled programming...

[kdog]

Sounds like impending doom for the limit that you tapped on - now might be a good time to hunt down a replacement, since the bullet has seemingly been dodged.

[sbdivemaster]

Wise advice, kdog. I will locate a back up today.

Been consulting Appliantology for years now, and I love it. While I was able to solve this one before getting help from some of the Grand Masters, I wanted to share what I learned for future Grasshoppers that may come along seeking wisdom.

[sbdivemaster]

Part procurred. # HH12ZB200 - $20 new on feeBay.

[kdog]

[Shootist]

If you pull the thermostat off the wall and the problem continues it isn't the stat.

If you were referring to the roll-out sensors by the burners those trip as an indication that too much heat is rolling back out of the burner tubes. It would be a good idea to take the door off of the burner compartment and fire the furnace up where you can watch the fire. Watch for a change in how deeply the flames are being drawn into the tubes once the blower engages. If any of the fire starts backing out the tube(s) even a little you may have a heat exchanger problem (or a restriction in the exhaust).

FYI....there are at least 2 and sometimes 3 of these sensors. The idea is that no matter what position these multi-position furnaces are installed there will always be one on top. Next time just swap the upper sensor with the bottom one if the top one is acting up.

Edited April 5, 2012 by Shootist