Gas furnace briefly shutting down

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Old 01-01-10, 08:24 AM
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Gas furnace briefly shutting down

Hi,

I have an induced gas furnace w/intermittent electronic spark ignition that's about 15yrs old. The furnace will run fine for quite a while trying to reach temp but before it gets there it will shut down. It doesn't shut down completely though. The draft inducer motor continues to run and it will restart within a minute (the pilot goes out and relights). Always restarts on the first attempt. The blower motor does not stay on (unless I keep in to "on" mode).

When its very cold and running for a long time it will do this several times before reaching the desired temp. When it doesn't need to run very long to get to temp it doesn't happen at all. I tried the following:

New T-stat
New filter
Clean furnace/burner area
Clean evaporator coils
Clean flame sensor
Open all dampers

I thought it might be a high limit switch but the blower isnt staying on to cool the area.

Any idea what this might be? Neither HVAC tech could figure it out.
Thanks.
John
 
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Old 01-01-10, 08:48 AM
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What is the make and model of the ignition control?

What does the pilot burner flame look like? Is it like a small blowtorch with a blue flame or more like a candle flame that is easily blown around?

Did the repairman measure the DC microamps flowing to the ignution module, and if so what was the read?

Is there a pressure switch on the furnace, and if so is that opening to shut off the burners?
 
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Old 01-01-10, 08:58 AM
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Originally Posted by SeattlePioneer View Post
What is the make and model of the ignition control?

What does the pilot burner flame look like? Is it like a small blowtorch with a blue flame or more like a candle flame that is easily blown around?

Did the repairman measure the DC microamps flowing to the ignution module, and if so what was the read?

Is there a pressure switch on the furnace, and if so is that opening to shut off the burners?
The ignition module is a honeywell s8600m. The pilot burner is like a small blowtorch. Unfortunately I dont know what his reading on the module were. I dont think there is a pressure switch on the furnace.

I think the problem the techs had was that it is intermittent. It did happen when they were here but it just starts right back up after it goes out. Always the same. Inducer motor on, blower motor off, starts within about a minute.
 
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Old 01-01-10, 12:29 PM
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Lazy and marginally competent repairman tend to be the ones to claim "Oh, my goodness! The problem isn't there right now so I'm HELPLESS to determine what it is!"

Intermittent problems often reveal themselves to good diagnostic methods. Not always, but often.

Does the fan motor keep running for a normal amount of time after the burners shut off too early, and then stop?

Checking the limit switch with and AC voltmeter to verify that it's not shutting off the burners would be a routine check to make to eliminate that as a source of the problem.
 
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Old 01-01-10, 02:20 PM
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Thanks for the reply.

I don't think the blower is running for the usual amount of time. I was only near it once when it shut down and the blower went off also. I have 2 identical systems (1st and 2nd floor) with the same honeywell circuit board and ignition module. Is the problem likely associated with one of these? If so I can have them substituted out one at a time to isolate the problem.
 
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Old 01-01-10, 02:43 PM
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I would first try switchig tstats and see if the problem is still evident or if it moved to the other system.

Blower shutting off points me to the stat.
 
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Old 01-01-10, 02:50 PM
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3 key things I am picking up on: You have an inducer motor, meaning more than likely it should have a pressure switch. I personally have not seen a furnace with inducer, yet no pressure switch. Even water heaters with inducers have a pressure switch.

You say you have a pilot and burner that goes out prematurely,

Your blower goes out. And you also mention it occurs when it is cold (I presume the house has gotten cold).
....................................................................


You say you cleaned the flame sensor. Where is that located? On the pilot assembly or is there another (also?) at far other side of the burners (usually right side)?

The blower may be going out simply because the house is too cold to keep it going. When it kicks on and draws cold house air through the furnace and the burner goes out, the temp may drop enough to shut the blower off. Therefore this may not even be a problem.

Look for any cylinder or diaphram looking device, metal or plastic, that has a 1/4 inch tubing hooked to it. That would be the pressure switch. And they mount these in the large door burner and inducer compartment.
 

Last edited by ecman51; 01-01-10 at 03:21 PM.
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Old 01-01-10, 03:13 PM
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Originally Posted by Jarredsdad View Post
I would first try switchig tstats and see if the problem is still evident or if it moved to the other system.

Blower shutting off points me to the stat.
I tried changing out the t-stats but it still occurred. The blower does shut off when this happens but it will stay on if I leave the blower in the "on" position on the t-stat.
 
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Old 01-01-10, 03:28 PM
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Originally Posted by ecman51` View Post
3 key things I am picking up on: You have an inducer motor, meaning more than likely it should have a pressure switch. I personally have not seen a furnace with inducer, yet no pressure switch. Even water heaters with inducers have a pressure switch.

You say you have a pilot and burner that goes out prematurely,

Your blower goes out. And you also mention it occurs when it is cold (I presume the house has gotten cold).
....................................................................


You say you cleaned the flame sensor. Where is that located? On the pilot assembly or is there another (also?) at far other side of the burners (usually right side)?

The blower may be going out simply becasue the house is too cold to keep it going. When it kicks on and draws cold house air through the furnace and the burner goes out, the temp may drop enough to shut the blower off. Therefore this may not even be a problem.

Look for any cylinder or diaphram looking device, metal or plastic, that has a 1/4 inch tubing hooked to it. That would be the pressure switch. And they mount these in the large door burner and inducer compartment.
Yes it does have a diaphram shaped pressure switch that is connected to the inducer motor by a tube. The flame sensor is on the pilot assembly. I had the entire burner out to clean the area. It's the only one. The pilot will always light without fail and it will run for long periods before the first shut down (45min). After the first shutdown it will shut down multiple times before reaching the temp (the intervals between shut down seem to get shorter)

What I mean by cold is that it occurs when the system needs to run to raise the temp for more than 3 degrees. I turn the temp down at night and when I leave during the day (about 5 degrees) Although it occasionally happens during its temp maintenance cycle after it has reached temp and is just maintaining the temp, I notice it most when it has been running for a while trying to get to temp.
 
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Old 01-01-10, 03:32 PM
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Ok, so this thig is shuting off on something. Make, model, serial number? It's not a safety (maybe) as it would lockout. Gentlemen, we have a mystery to solve.

Multimeter would be helpful also.
 

Last edited by Jarredsdad; 01-01-10 at 03:51 PM.
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Old 01-01-10, 03:55 PM
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Originally Posted by Jarredsdad View Post
Ok, so this thig is shuting off on something. Make, model, serial number? It's not a safety (maybe) as it would lockout. Gentlemen, we have a mystery to solve.
The system is about 15 years old and I dont have much info on it. I did some searching with the info that was on it but I couldnt find much. No specific name is listed on it.

Intercity products
Manuf #1172489208
Model# NHGE075CF01
Serial# N920610709

It is a mystery. I thought a limit switch but the blower goes off. It's like it either not sensing gas or the gas is shutting off.
 
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Old 01-01-10, 04:15 PM
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Jumper "R" to "W" at the stat or TH to TH at the furnace. Does the furnace and blower stay on?
 
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Old 01-01-10, 05:09 PM
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Originally Posted by Jarredsdad View Post
Jumper "R" to "W" at the stat or TH to TH at the furnace. Does the furnace and blower stay on?
Yes they both stay on until I remove the the jump. I don't know whether this would prevent the system from shutting down since it is at the temp setting. Should I try this in the morning when its trying the reach setting temp?
 
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Old 01-03-10, 06:05 PM
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The jumper is simulating a call for heat from the stat. Looks like it's a stat problem.
 
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Old 01-04-10, 03:16 AM
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Originally Posted by Jarredsdad View Post
The jumper is simulating a call for heat from the stat. Looks like it's a stat problem.
I changed out the t-stat and had the same problem. I tried jumping it when it needed to run for a long time to reach temp and unfortunately it did the same thing, shut down and restarted a few times.
 
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Old 01-04-10, 07:03 AM
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Here is the lierature for the control:

http://customer.honeywell.com/techli...it/69-1954.pdf

Under other circumstances I would look at replaceing this. But since your indoor fan is also shutting down it still points me to a loose or broken wire in the control circuit.

As long as "R" is connected to "W" everything should be runnig. If the flame goes out, air switch opens etc,. the indoor fan should stay on and the control will continually try to light every 5 minutes.

Outside of the box, can you use a multimeter to monitor the transformer output? During the entire cycle does it stay around 24 volts? Does it fluctuate and dip as low as 18 volts?

If the trans if failing and gets down to 18 or below, this will cause everything to shut down.

Shot in the dark...
 
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Old 01-05-10, 07:09 AM
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Originally Posted by Jarredsdad View Post
Here is the lierature for the control:

http://customer.honeywell.com/techli...it/69-1954.pdf

Under other circumstances I would look at replaceing this. But since your indoor fan is also shutting down it still points me to a loose or broken wire in the control circuit.

As long as "R" is connected to "W" everything should be runnig. If the flame goes out, air switch opens etc,. the indoor fan should stay on and the control will continually try to light every 5 minutes.

Outside of the box, can you use a multimeter to monitor the transformer output? During the entire cycle does it stay around 24 volts? Does it fluctuate and dip as low as 18 volts?

If the trans if failing and gets down to 18 or below, this will cause everything to shut down.

Shot in the dark...
I tried leaving the blower in the "on" position on the stat. The furnace still shut down as its been doing but the blower remained on. Also there is no consistency to the problem other than it occurring when the furnace has been running a long time. Once it shuts down/relights the first time it'll happen again in much shorter intervals before the temp is reached.
Does this still seem like a loose or broken wire?

Thanks.
 
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Old 01-05-10, 07:38 AM
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Well, JDW, you have some things you need to test to identify the problem.

I agree with Jarred that it sounds like a bad Honeywell ignition module.

But the symtom could also be caused by a pressure switch (if any) that is opening or a high temperature limit switch that is opening. An erratic power supply to the ignition module could be causing a problem.
 
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Old 01-05-10, 02:26 PM
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Can you read the wiring diagam on this thing? Can you post a picture of it?

Seattle - fan/limit switch is the only thing I can think of (actually to just smacked me upside the head) that would produce this problem. Having the fan on takes it out of the fan/limit (heat) circuit.

jdw - Intercity turned into I.C.P or International Comfort Products and the parent of several brands. Google them and see if they can email a pdf of the diagram if you can't post a pic of the one in the furnace.
 
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Old 01-05-10, 03:42 PM
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I called a few places. Your model number matches the serial. It was sold by Servicemen (s) Supply. But I can't find a diagram.

If you can't post one cal FastParts at 1-866-380-3278 and ask if they can email one. Tell them you out in the boonie and the hvac guy won't work on it without a diagram or something.
 
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Old 01-05-10, 03:58 PM
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Originally Posted by Jarredsdad View Post
I called a few places. Your model number matches the serial. It was sold by Servicemen (s) Supply. But I can't find a diagram.

If you can't post one cal FastParts at 1-866-380-3278 and ask if they can email one. Tell them you out in the boonie and the hvac guy won't work on it without a diagram or something.
I really appreciate all the help. I found a diagram on the cover that protects the circuit board. It reads standard heating and cooling diagram. I took some photos and will try to get it readable.

I changed out the ignition module on the off chance that is the problem. At least doing little things like that are easy with identical systems.
 
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Old 01-05-10, 03:59 PM
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Yes, the pressure switch 24 volt power coming into it, and leaving it, needs to be tested during failure. If no volts in or out, means problem not pressure switch related. But if 24vac power in, but not power out, means many things can be wrong involving the draftiing of the furnace, or the pressure switch itself (although usually that failure is rare). Very important for us to learn of the voltage readigns at that PS, please, so we can hone in on THAT cause, or move to something else.

Circuit boards get replaced when either all other tests have been exhausted, or you can actually spot where something has arced on the board. Or you have money to burn, and are willing to take a risk.
 
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Old 01-06-10, 08:32 AM
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Originally Posted by ecman51` View Post
Yes, the pressure switch 24 volt power coming into it, and leaving it, needs to be tested during failure. If no volts in or out, means problem not pressure switch related. But if 24vac power in, but not power out, means many things can be wrong involving the draftiing of the furnace, or the pressure switch itself (although usually that failure is rare). Very important for us to learn of the voltage readigns at that PS, please, so we can hone in on THAT cause, or move to something else.

Circuit boards get replaced when either all other tests have been exhausted, or you can actually spot where something has arced on the board. Or you have money to burn, and are willing to take a risk.
The problem is so intermittent that I'm having a problem testing as the shutdown occurs (very cold sitting in the attic for long times). If I notice it occurring frequently I go up to check but nothing yet.

I changed out the ignition module but still have the problem. I don't mind switching parts between the furnaces. I'll try the pressure switch and eventually the circuit board (you're right they are expensive, I had one burn out last year)

I appreciate everyone's help.
 
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Old 01-06-10, 08:49 AM
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Often intermittent problems can be caused to occur by one of two methods:

1) repeatedly cycling the furnace on and off to give the furnace systems a chance to fail. Doing this 50-100 times may give the intermittent problem a chance to display itself.

2) Turning the thermostat 'way up to cause the furnace to run continuously for a half hour or so.
 
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Old 01-08-10, 05:17 AM
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Originally Posted by SeattlePioneer View Post
Often intermittent problems can be caused to occur by one of two methods:

1) repeatedly cycling the furnace on and off to give the furnace systems a chance to fail. Doing this 50-100 times may give the intermittent problem a chance to display itself.

2) Turning the thermostat 'way up to cause the furnace to run continuously for a half hour or so.
Run time to reach temp isnt an issue. It seems to take forever to reach temp. If some of the warm air would stay downstairs it wouldn't work so much.

I was trying to wait out the shutdown to check the pressure switch as you all suggested but it didnt shut down so I just changed the switch out. It's been about two days and it hasnt shut down yet. Hopefully that was my problem.

Thanks for all the suggestions I wouldn't have changed out the switches without them.
 
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