Arcoaire Furnance Overheating

I woke up this morning to a cold house, no furnace. When I checked the control it showed a "hi-limit" fault. I shut it down and let everything cool down. I checked for obstructions and couldn't find anything so I fired it back up. Now it won't run a cycle.

It starts the forced draft motor, lights the igniter, fires and burns. The flame looks good. It burns for a 10-15 seconds and then everything shuts down including the draft motor. It sits for a bit and the the draft motor kicks on, but shuts down almost immediately. The control is not showing any fault codes. Does it need to run through several of these failed cycles before it registers a code?

Any thoughts on where I should be looking? I checked all the sensors with my multimeter and they are all open/closed like they should be when the furnace is not running. (I thought maybe one might have gone bad)

This afternoon I put in new filters thinking maybe reduced airflow caused the overheat this morning. The furnace ran fine for about 15 minutes and then the hi limit switch kicked out. Rather than just shutting down the flame and allowing the blower to cool the furnace everything shut down. Should this have happened?

I am going to clean the blower motor and furnace this weekend in hopes that will help the airflow through the furnance.

Any other thoughts/suggestions?

My furnace is model GDH100A016IL.

 

Seems odd that the draft motor & circulating fan shut down on a high limit situation. Normally the circulating fan will kick into high speed & the venter will keep running.

 

I'd check the thermostat circuit, first off. Furnace should not limit in only 10-15 seconds and have ID shut off, as Grady said. ID's shut off when thermostat power goes away.

 

I'm sorry. The furnace wasn't high limiting in 10-15 sec. The draft motor kicking on and then back was after it hi-limited this morning.

It ran fine for about 15-20 min this afternoon before hi-limiting and when it did everything shut down.

I had to go to work so I haven't had a chance to do anymore troubleshooting.

I'm planning on cleaning the burners, blower wheel, heat exchangers, etc this weekend. Right after we first moved in, 9 years ago, I remember having similar issues and the burner chamber was sooted really bad. I'm wondering if the same thing hasn't happened again.

I read in another forum that these furnaces have issues with sooting up and you should clean the burners every couple years. Which I'd discovered that a couple years ago!

 

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There are several things that can cause high limiting.

Some furnaces simply have that propensity, after they run and run a long time - that the temp gradually creeps up there.

I have a furnace that high limits after about 8 minutes - improved from 3 minutes! I gave up on it, and figure that now that temps are equalized in house, that during normal cycling operations, it may not run long enough to high limit (unless maybe when way below 0). But it would if someone set the heat way back, say at night, and tried to warm the house up to temp. On that house, the limit switch itself was tested, it was then replaced (wasn't cause), the secondary exchanger fins were cleaned, the blower vanes were cleaned, the filter was removed, the registers all open, (can't tell if duct dampers since basement ceiling finished off!),the blower door left off, the a/c evaporator coil checked and cleaned(not the issue) - yet it still limits in 8 minutes. Gas meter timed test was just about right on the button, as far as input btu consumption also, so too much gas is not the issue either. Burner flame size, cone size and color also looked quite normal to me. And heat exchanger inspection, with burner tubes out, did not show any soot in area of primaries.

I wish you better luck when addressing everything I did. Oh - how did I improve it though by almost 200% compared to what it was? It turns out that the burners were all plugged with rust scale except for under the limit switch. All the burner fire as raging under the limit switch! Now the burner tubes burn even blue flames throughout their length.

 

I'm starting to wonder if the control board isn't bad. This morning when I got up the furnace was firing the draft motor for about 2-5 sec and then immediately shutting off. I stood by the furnace and was watching for an error code and exactly what was going on. It fired the draft a couple times and then it fired the draft motor, let it run and even fired the ignitor before immediately shutting down. It would never give an error code. I decided to turn off the ac power for a while and then turned it back on. Same thing, it would start the draft and then shut down. I decided to let it go for a while to see if it would generate an error code. Miracously after several fails it fired and the blower kicked on, but shut down after about a minute. I checked the hi-limit and it did not kick out. Again no error code was generated.

Would this be indicative of a bad control board?

 

I did some troubleshooting this morning. I decided to check the voltages at the 24v transformer and through the safety switches. I am getting 26V at the transformer and 20-24V at the safety switches. Is that okay?

After fiddling with that the furnace ran a full cycle with no problems. I'm at a loss here.

I'm gonna leave it on and see what it does today.

 

That would indicate thermostat/call for heat line opening up premature, or relay for ID releasing when it should not be, or glitch in ID, or yes - bad board.

 

Thanks ecman. Your posts, both in this thread and others I've searched, have been very helpful.

My board is supposed to have "self diagnostics", could it be bad without triggering the LED?

Also, if I want to jumper the thermostat, what 2 wires do I jumper to make it call for heat?

Weird thing is it has run 2 complete cycles without any problems. I'm starting to think I jostled a loose connection when I was checking the voltages on the transformer. I also checked all the connections on the board while I was at it.

I'm planning on cleaning everything tomorrow, it needs it anyway.

 

EC doesn't seem to be available just now so maybe to help a bit I thought I'd jump in.
To by-pass the t-stat you jumper terminals R & W for heat.

 

Thanks Grady!! I thought maybe "red" for heat, but wanted to make sure. LOL

 

Actually Red is power, white is heat, green is fan, & yellow is the outdoor A/C unit.

 

Well, as of now everything is working as it should! Go figure! I can only figure that I had a loose connection at either one of the terminals or inside the board and when I pressed on all the wires it corrected itself. I found that White Rodgers makes an universal board that will work with my furnace and it's only around $120, sure beats the $300 for an OEM board (which is probably a relabeled White Rodgers)!

I think the overheat and shut down issues were 2 seperate issues that happened to manifest at the same time. I'm gonna clean out the furnace tomorrow so hopefully that will fix the overheat, although it hasn't done it today.

Thanks for all the help! I'll be back if it starts acting up again.

 

By all means -jump in. I'm going crazy responding to all these threads, especially with the site being slow. It works on my nerves when I can't go fast enough. Definitely appreciate more help.

 

Well, I cleaned it out today and problem continues....see this thread: http://forum.doityourself.com/gas-oi...ml#post1786575