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Old 11-30-2013, 09:45 AM   #1
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Furnace not keeping temps overnight


I have a York Diamond 80 gas furnace which stops heating at some point each night the temps drop below freezing. For example, I have my thermostat set for 72 which is maintained throughout the day ( I can see and hear the furnace lighting and running). At some point during the night the furnace will no longer start up with the thermostat showing 67 deg or less and the burner symbol being displayed on the thermostat indicating the thermostat sent a light signal. I've used sand paper to clean the flame sensor and I've replaced the capacitor even though the blower has been working fine (the capacitor didn't look in good shape and my meter is showing inconsistent readings on it). If I turn off the unit from the thermostat then back on, the heater will start up fine (blower, fans, ignitor all work normally) but I have to keep doing this until the in door temps get a little higher to about 70 or more. I have not seen the LED indicator showing an error code when the furnace has stopped working.

My next step is replace each of the 3 limit sensors placed around the burner (they don't look resettable) as well as the flame sensor. Is this a reasonable approach? What is the next step?

Thanks.

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Old 11-30-2013, 02:38 PM   #2
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Furnace not keeping temps overnight


Quote:
Originally Posted by shokwavxb View Post
My next step is replace each of the 3 limit sensors placed around the burner (they don't look resettable) as well as the flame sensor. Is this a reasonable approach? What is the next step?

Thanks.
I can guarantee that won't fix what ever is ailing the furnace. The limits are for flame rollout protection. If they trip, the furnace won't run at all until they are either replaced or reset manually. The flame sensor either works or doesn't work. It only comes into play once the burners are lit. It has nothing to do with the start sequence of the unit.

What kind of thermostat do you have? Electronic or old mercury tilt switch? Does the thermostat have a timer in it? Do you have a volt/ohm meter? If so, it is time to get some voltage readings on the system when it is acting up. It could be a temperature related problem with a transformer or the board itself.

When you say the thermostat is showing 67, is this the temp you have it set to at night? If so, what happens if you leave the thermo at 72 during the night.


Last edited by danpik; 11-30-2013 at 02:41 PM. Reason: more questions
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Old 11-30-2013, 04:51 PM   #3
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Furnace not keeping temps overnight


Quit throwing parts at your furnace and actually diagnose it. In order to do so you must either catch it in the act of failing or catch it at a time that it shows a diagnostic code to help lead you down the path of the correct diagnosis.
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Old 11-30-2013, 05:00 PM   #4
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Furnace not keeping temps overnight


Who wants to spend the night looking at a furnace? If there is fault then the board code should maintain until the morning.

Since the board doesn't show an led error code then the fault will likely be with the thermostat/ thermostat wire connections or the board itself.
An unlikely exception to this is if your board led light is fried and won't light up with any cause. You can test this by deliberately inducing a fault (disconnect the flame sensor to see if the board shows an led fault.

Because the problem is intermitant, I'd start by making sure the thermostat connections are tight and that your physical resetting of the thermostat is not just making and breaking the electrical connections.
Next...on put a new thermostat.
and if that doesn't solve it ...... a new board through a reliable source.

Last edited by how; 11-30-2013 at 05:05 PM.
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Old 11-30-2013, 05:51 PM   #5
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Furnace not keeping temps overnight


I forgot to ask if you can observe the board led without having the door switch shut off the power to it.
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Old 11-30-2013, 06:11 PM   #6
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Furnace not keeping temps overnight


Boards will auto-reset after 3 hrs unless it is a critical fault. Post a closeup pic of the burners and flame sensor. On those yorks the signal has to jump from the sensor to the steel plate of the furnace in front of the burners and then it goes thru the metal back to the board thru grounding. not thru the burners like other furnaces. you have to take some steel wool and clean the closest metal to the flame sensor in front of it so it shows raw metal. You probably have a weak flame signal. You are VERY VERY lucky SMAGS post below your post has the same furnace and I got the pic and put a red arrow for you. Clean that metal in front of the flame sensor. Clean the sensor again with steel wool as sandpaper will leave a residue.
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Last edited by yuri; 11-30-2013 at 06:20 PM.
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Old 11-30-2013, 06:27 PM   #7
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Furnace not keeping temps overnight


@Yuri
Check my reasoning
If the board auto reset after 3 hours, why wouldn't the furnace not then try to fire up with that thermostat calling for heat. I think the op is saying it didn't.
The fact that it didn't either fire up after auto reset or show a led fault code for why it didn't is why I was suggesting either a board fault or a problem with the board not receiving a thermostat signal.
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Old 11-30-2013, 06:38 PM   #8
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Furnace not keeping temps overnight


After way too many yrs of listening to customers and posters vague explanations of what they think is wrong with their furnace and some cannot literally see the LED etc I have learned to just go with the most obvious problem and tell them to try that and start there. At night the air is colder and heavier and the draft changes and so does the flame pattern. that will move it away from the sensor and if it is at the tripping point then that little nudge is all it takes. Hopefully we will get some feedback if he tries it. Probably about 5% of the techs out there know what flame rectification REALLY is or how it works. anybody can clean a sensor but only a skilled tech knows what it does or how. no pun intended.
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Last edited by yuri; 11-30-2013 at 07:12 PM.
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Old 12-01-2013, 09:41 AM   #9
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Furnace not keeping temps overnight


I've had some success for one night anyway (I may have another issue described further below). After I posted my original question I looked at my furnace some more and found where the pressure switch hose attaches to the furnace (inducer?), the inlet into the inducer from the pressure switch was completely blocked. I used a paper clip to clear the blockage and blew through the tube after reattaching to make sure air was moving through. After I did that I set my thermostat for 70 for the night.

Last night the outside temps went down to about 21deg. My furnace kept up the inside temp to what I set for (70deg) and I was able to set the temp to 73 and have it reached earlier this morning. This is a big improvement over what had been happening. I'm not sure if I have another problem now though. As I found out yesterday, the LED could barely be seen through the window in the door panel. I had to press my face up to the hole making it dark before I could see the faint flashes. I pulled the front panel off and taped the door switch closed so I could see the LED clearly as the unit ran. I don't see any flashing from the LED until the furnace shuts down after having a flame going for several minutes. At some point the flame goes out and I see 4 blinks on the LED ("High Aux. or Spill limit switch open"). After maybe 5 - 30 seconds of the LED blinking it stops the 4 flash blinking. I have the blower on continuously so it keeps putting out warm air through the vents. The furnace will relight successfully later on (20 minutes roughly) as it maintains my set temp.

*** Is this cycle normal with the flashing LED? The furnace running until some temperature limit is hit internally then shutting down for a break as the furnace cools down and then relighting later?

So far I've only replaced my capacitor as it had some kind of greasy/gunky residue all around the ground facing side of the contacts and I was getting inconsistent readings when testing it with my meter so decided to replace it. I've also pulled out and cleaned my flame sensor with sand paper and cleared the blockage from the pressure switch to the inducer. Air filters are new and clean. At one point during my testing I noticed the flame went out almost immediately. While doing my research into my heating issue I saw this was possibly due to the flame sensor needing cleaned or replaced. So that's why I cleaned that as much as I could.

Last edited by shokwavxb; 12-01-2013 at 10:03 AM.
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Old 12-01-2013, 10:01 AM   #10
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Furnace not keeping temps overnight


You got a whole gamut/series of problems.

1) clean that metal close to the sensor or you will get a weak flame signal and remove and clean the burners by blowing compressed air thru them and then flushing them with hot water in a sink and drying them
2) I was going to mention that pressure switch port issue but fortunately you got it done
3) If the high limit is cycling on/off then you have poor airflow thru the furnace from a dirty AC coil or the fan not going fast enough or small ducts. Stick a cooking thermometer in the duct 2 feet downstream from the plenum and subtract the return temp or house temp and get the temp rise reading from the model sticker and compare. You should replace that limit control soon as it will stick open and fail soon. americanhvacparts.com should have it
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Last edited by yuri; 12-01-2013 at 10:03 AM.
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Old 12-01-2013, 11:13 AM   #11
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Furnace not keeping temps overnight


Thanks Yuri. I checked my AC coils and they looked caked over with dirt from underneath where the air would come up. I can feel how not much of the rush of air from the blower is making it above the coils.
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Old 12-01-2013, 11:20 AM   #12
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Furnace not keeping temps overnight


then you need to clean that coil with a soft brush and vacuum and then spray it with Simple Green citrus based cleaner and then flush it with lots of clear water. I would get a spare limit control as they are cheap and weak and it will possibly fail on Xmas day or when you least expect it.

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