Furnace Question

rlk · Nov 10, 2003

Dave, I had a similar problem with my propane furnace last winter. Turned out that the condensate drain was plugged. Once we took the condensate line apart and blew it out, we had no more problems. This was a very simple fix, but was hard to diagnose. When the condensate would build up and could not get out the furnace would cut off. Slowly the condensate would drain out, and by the time the service person came the condensate had drained out, so it took them forever to find the problem. The person who eventually figured out the problem just stumbled on it. They had tried so many things that out of desperation he took the condensate line apart and found that it was about 99% blocked.

Don't know if this is your problem or not, but your description sounds almost identical to mine.

Bob

ns_in_tex · Nov 10, 2003

Try cleaning the flame sensor, Also check wiring polarity and Is unit grounded good?

dieselsmoke1 · Nov 10, 2003

( Right now, the furnace will light and fire up for 1-2 seconds and then shut down and cycle continually. )

I had a similar problem with a natural gas unit. A dirt dobber had blocked the air vent on the pressure regulator, the unit would fire for a couple of seconds till the gas presure fell off, then the flame sensor would shut it down and the control circuit would recycle.

gsganzer · Nov 11, 2003

I think everyone's given you good advice. Check the condensate drain, flame scanner (or thermocouple) and pressure switch.

A forced air furnace is a pretty simple apparatus. They almost all follow this start sequence (depending on configuration).
1. Command to start from thermostat
2. Blower starts for air purge (usually requires 4 air exchanges)
3. Glow plug energizes (if no glow plug goes to step 4)
4. Gas valve opens (standing pilot or igniter ignites gas)
5. Flame scanner detects flame or thermocouple (temp. switch) indicates flame, keeping gas valve open.

There are usually a couple of permissives needed to keep the gas valve open. Usually gas pressure and fan air flow (might monitor fan amperage for flow indication) as well as the flame indication. Otherwise, you get a "fail to start" indication and the unit resets.

If your furnace fires but then trips out, then you can start the troubleshooting from step 4 and try to isolate it to the flame scanner/temp. switch, gas pressure switch, airflow switch. Hopefully it's just simple troubleshooting (isolate and solve).

thcri · Nov 11, 2003

(
Right now, the furnace will light and fire up for 1-2 seconds and then shut down and cycle continually. We have had 2 different servicemen out and neither can find anything wrong other than it just doesn't continue to run.
)

Dave if this is the Bryant furnace with the 733 pilot assembly I would replace that pilot assembly. One of the big problems with that pilot assembly was that it proved pilot and lit the main flame, but the cool air now going over the pilot cooled it back down enough to shut the system down and then it would go through its start process again. We even had some that were so bad with this that we drilled the orifice out one notch to get a warmer flame. I would also check and make sure your gas pressure is up to snuff and if anything on the high side. Your short cycling can be caused by other things but this was one of the most commom causes with that furnace. I was just in Green Bay a few months ago, if I would have known your were having trouble I would have stopped in.

murph

Old_Hickory · Nov 11, 2003

( If you have neighbors at your cabin you can buy this little device that turns on a lamp when the temperature drops below a certain set point. )
I would hook 2 lamps/lights up that way if one burns out you will have another light to view.If you only had one light and it burnt out,your neighbor might think everything was ok.

DocHeb · Nov 11, 2003

Same problem with a Comfortmaker >90% furnace, first winter after installation.

Problem was intermittant - first two service calls "couldn't find anything".

Third (and final) serviceman was the most experienced. He thought he heard a "little splash sound that wasn't right". It ended up that the air blower that purges the combustion gas worked well, but a small drain at the bottom of the blower chamber was plugged with PVC chips from the furnace installation. If the furnace was running for some time, then restarted quickly, the slowly draining chamber didn't have time to empty and the furnace wouldn't cycle. Cleaned out the chips, everything ran fine.

On another high efficiency furnace I had the combustion chamber blower was making noise. The screen on the outside exhaust pipe had fallen out, and a sparrow had followed the pipe in, only to fall into the combustion blower. The serviceman said it was a common occurance.

yooperdave · Nov 17, 2003

Hi Murph,

The 3rd time is a charm /forums/images/graemlins/smile.gif!

The Carrier repair man replaced some kind of assy which included the gas valve and a small circuit board which plugged into it.

All I know is that there is now heat when I want it.

Thanks to all.

Yooper Dave

thcri · Nov 17, 2003

Glad you got it going.

murph

heehaw · Nov 18, 2003

its probably to late..but some of the best equipment around, and very few people have heard of them, is goodman..they just entered the home market a few years ago, and do no advertising, that i have ever seen anyway...price is right and the 2 i have had anything to do with, seem to just keep on working...
heehaw