Furnace question

[cocheese 0]

My furnace will turn on and start the flame sequence then it will shut itself down after about 8 seconds. Then it tries it again a minute later. This goes on for 10 minutes then it stops trying and leaves the internal (small) fan on for hours if I'm not home to turn it off.

If the exhaust pipe is cold( furnace not used for quite some time) there is no problem and the cycle starts and stops just fine like there is no problem. But on the next cycle, the auto shut down happens during start up.

It doesn't work when the exhaust pipe is warm. What is the problem? Fumes are not escaping the system quick enough? Clogged vent?

My filter is new. The cheap kind. Problem was present with the old super filter also.

[Lindercles 0]

What is this "furnace" you speak of?

[cocheese 0]

It's what we of the north use in the winter to avoid having to bother you southerners. So yea, you want me to get this fixed.. or else.

[jkm2500 0]

This could be a plethora of problems. Some things to check.

Make sure that none of the wiring is touching and creating a short. If this is the case a little bit of electrical tape should insulate the wire and prevent the problem from occuring.

There is a flame sensor. It tells the control unit that the burner actually lit. It looks like a little probe that hangs directly in front of the burner tray. Use some emory cloth to clean the surface, and then make sure that the wiring is properly routed and connected.

If the CU fails on the light sequence the furnace will go into a safety mode, it will shut down the burner and leave the exhaust fan blowing to make sure that there is no gas collecting in the burner area.

one last thing to check depending on whether there is a pilot light or ceramic ignitor. If there is a pilot light make sure that it is lit. If there is a ceramic ignitor, make sure that it is intact. If it is cracked or fouled, the CU will take the furnace through 3 attempts to light the burner then go into saftey mode. The CU will reset (on some models) and attempt this again after 10 mins or so.

If none of this helps, reset the unit by turning it off for a few minutes then turning it back on. There is a light on the CU that will blink a fail code. If the CU is bad you may not get a code. When you take the cover off the unit you must hold the safety switch depressed in order to get the unit to cycle. There shouldnt be any reason why the unit would work when the exhaust is cold and not when its hot.

I am not a technician, but I did stay at a Holiday Inn Express last night. Let me know if any of this helps.

I have found that it is cheaper to check everything prior to calling a repair guy. They usually charge 100 for the service call, and a ceramic lighter is only about $25.

The primary purpose of the Armed Forces is to prepare for and to prevail in combat should the need arise.

[DeNReN 0]

do you have a manual for the furnace?

have you tried looking online to see if there is a manual avaible?

and you havent given enough info...ie: oil fired?/gas? ...make,model,age,etc........

one must understand how something is supposed to work before they can properly diagnose it...hence the manual.

[stitch 0]

Maybe you need to load that coal you got in your stocking in it.

"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

[cocheese 0]

Ceramic ignitor. There are no lights. I'll look for a flame sensor and clean it. I'm aware of the saftey cover switch etc.

I tried to mess with the fan temp dial with the slides in the slots of the dial.

The sytems doesn't work when it is warm . Why?

[cocheese 0]

It's a natural gas, forced air, electric ignition.

Amana "Air command"80.

No manual.

[dbattman 0]

I can take a stab at it-

Is there a temperature sensor somewhere that could be failing and shutting the furnace down? If it thinks it is too hot it will prevent a restart.

[The_Don 0]

Hit the top near the exhaust pipe. Hard!

Do you hear rust falling ??

I am NOT being loud.
I'm being enthusiastic!

[icarusfx99 0]

If it is a high efficiency furnace (90+) with external air intake, you should also check and make sure that the furnace gets enough combustion air.

[cocheese 0]

The pipe does have some white corrrison powder. Not too bad on the rust falling etc.

[cocheese 0]

There is a temp dial near the burner for fan timing.
I've been trying different settings.

[dbattman 0]

Yeah, I'm thinking there should be something internal to the furnace. If it gets too hot, you'd want it to shut down so it doesn't burn up.

Why it's thinking it's too hot would be the question- bad sensor or reality?

[cocheese 0]

I found the flame sensor and will take that out and clean it. Should i bend it more to the center of the flame as it is only on the edge of it.

It's working fine right now, but I tried to turn it on again after a good cycle and it still had the problem of shut down. Then I waited 15-20mins for cool down and tried it again. It's on.

So if the time between cycles is short, it doesn't work.
Apparetly the house cools faster than furnace. So i will try to cool the furnace by leaving the door open and maybe a fan in there to circulate the air and cool it.

Could the flame sensor be bending away from the flame when it is warm? then returning to a workable position when it is cold?

[matt1215 0]

Quote

...if the time between cycles is short, it doesn't work. Apparetly the house cools faster than furnace. So i will try to cool the furnace by leaving the door open and maybe a fan in there to circulate the air and cool it...

You could also adjust your wall thermostat. Digital thermos have a "Span" setting (my Hunter thermo will span 1-3 degrees, accessed by holding down + & - at the same time). Mechanical thermos have an adjustment on their coil that'll adjust span on the heat side only.

[Daane 0]

Jeff why havent you called goat yet

[dbattman 0]

Now, I'm just thinking here and I'm not a tech.

There's a heat exchanger between the burners and the forced air since you don't want to vent the burner gases to the house. Somewhere in there should be a temperature switch or thermocouple to prevent the overheating of the system. So it could be that one of the sensors has gone bad or the high/low temperature settings are off. If it triggers on a high limit it is probably set to wait until it trips a low limit before it will start.


So, bad sensor or deadband adjustment?

[DeNReN 0]

I took a quick look online for more info but got bored ....I did however find these forums....prob get a better answer there then here

http://www.hvacmechanic.com/forums/forums.htm

[PWScottIV 0]

I think I might actually know what's wrong. There should be a pressure switch that makes sure the fan is operating properly. The rubber diaphram in the switch or the hose connecting the switch it to the duct could be leaking. The best way to make sure that's the problem is to short-circuit the pressure switch wire right after the fan and the burner starts. You cannot bypass it before then because the system might sense there is something wrong. Let me know if that works.

Gravity Waits for No One.

[SkydiveJack 1]

I had something similar to what you described a few years ago with my 1991 Lenox Pulse. This may or may not apply to your situation. I hope I can describe it clearly.

Mine has a 2 inch PVC exhaust pipe that comes out of the lower left side a few inches then hits a "T" fitting. The pipe going up from the "T" goes through some sort of expansion chamber then up through the roof. Going down from the "t" was about a 1 foot piece of PVC that terminated above the floor with a PVC cap.

My repair guy apparently knew exactly what was going on. He cut the cap off and rusty water came out. He explained that there is condensation in this pipe and there is a smaller internal pipe to take the water away to a drain. Over time, as the unit gets older some rust will develop and plug the small internal drain pipe. This somehow affects pressures in the system and I believe some pressure switches that someone else mentioned earlier. He replaced the old solid cap with a cap that has a threaded plug. I just drain it once a year (yes there is always rust) and all has been well.

Hope this helps!

[jumpinfarmer 0]

Sorry I only know oil furnaces and LP grain dryers.

I am happy to say though that I haven't used my oil furnace yet this year after installing a corn burning stove.

Good luck

[Broke 0]

YOu need a wood burning stove... mmm nice and toasty warm it will save you lots on your gas bill too

Divot your source for all things Hillbilly.
Anvil Brother 84
SCR 14192

[MrBrant 0]

Although I know more about commercial electric systems than residential gas - here's the 2 things I would check:


1. Auto-reset safety.
There will be an auto-reset safety (limit switch). If the temperature gets too warm, it will trip, and shut off the burners. This could be malfunctioning and tripping too soon.

2. air pressure switch. (big metal can with a diaphram and microsiwtch)
in home systems, I believe these are usually used to make sure the exhaust fan is running. Typically thease are very sensitve switches, and can fail.
To give you an idea, the ones used in commercial duct heaters usually have a trip point of 0.05 inches of water. (approx 0.035 PSI)


Those are the 2 things that come to my mind which could easily cause the cycling you describe.

[SkydiveStMarys 0]

Please call a professional. I wouldn't want anything to happen to my friend.


Bobbi

A miracle is not defined by an event. A miracle is defined by gratitude.