York Diamond 90 - Ignites but does not stay lit

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Old 11-18-11, 12:39 PM
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York Diamond 90 - Ignites but does not stay lit

I have a York Diamond 90 model number: P3URD12N07501A that fails to stay lit. This model does not have an external to the house pvc intake, the intake is a hole right on the box that houses the igniter. This issue just happened overnight, woke up to a cold house. Took several hours to get it to stay lit in the morning. Here are the symptoms:

1. Turn on the power switch to the unit
2. Coil lights up, a loud click sounds, gas flows, flame happen.
3. ~5 seconds later the flame dies.
4. The furnace repeats step 2-3 several times with identical results.
5. The blower stays on simply circulating cold air, the red light blinks 8 times to indicate that it failed to ignite.

I turned power on/off to the unit many times this morning until it finally stayed lit several hours later. Once I got it going it started turning on fine after that for several hours. Now it won't stay lit again.
 

Last edited by ChosenGSR; 11-18-11 at 01:01 PM.
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Old 11-18-11, 02:11 PM
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Very likely your furnace has a flame sensor. The ignition control turns the main burner gas on for 3-5 seconds after the hot surface ignitor has warmed up. If the flame sensor and ignition control don't detect that the burners have lit, the main burner gas is shut off and a new trial for ignition begins.

The most common reason for the flame sensor to fail to detect that the main burners have lit isd that it get coated with invisible oxides and the flame no longer can physically touch the flame sensor.

The flamwe sensor is typically on the opposite side of the furnace from the HSI. It's a thin rod sticking up into the areas where the flames burn, and connected to the ignition control with a single wire.

Remove the flame sensor and clean it with a wire brush or some fine sandpaper --- you don't need to cut into the metal, just clean the surface. Reinstall and try it again.

I'd clean the flame sensor annually as regular maintenance to avoid future problems.
 
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Old 11-18-11, 04:14 PM
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Thanks for the suggestion, I did just that and it fired right up from the first attempt! I will report back if the issue comes back and this just happened to be a fluke. Otherwise we can consider this case closed
 
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Old 11-19-11, 04:55 AM
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Ok so back to update, it seems that perhaps cleaning the flame sensor was part of the problem, however there are still issues, yet now are different in nature. Now when the furnace has idled for a while and had a chance to cool off it will fired right back up right away (looks like that initial problem was solved by cleaning the flame sensor).

However when the furnace gets hot, the following happens:

1. If it lights back up, it will burn for a while (~30 seconds), the gas "click" happens turning it off, the furnace reignite it, it will burn some more.
2. step 1 repeats itself several times until the furnace gets back into standby (8 ref flashes) or it finishes it's task bringing the temp back up to where it needs to be.

or sometimes

1. The lighting back up is not successful, but unlike in the original situation, the coil lights up, the gas "click" happens, it lights up and it's followed by frantic "clicking". It sounds almost like a bad relay.
2. The furnace will attempt to light it up again with similar results, there is no pattern to the "clicking" sometimes its literally several (3-4) within 2 seconds, sometimes they are farther apart.



If I turn off the furnace and let it cool for a while, it fires back up fine again with no problems (something it was not doing originally, before cleaning the flame sensor).
 
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Old 11-19-11, 05:58 AM
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When the furnace lights up, it should stay lit until the thermostat shuts off the furnace.

You either have a furnace sensor shutting the furnace off for a reason or you have a bad ignition control board. Probably a bad ignition control board.

But you should use an AC voltmeter to check to see if sensors like the pressure switch are opening to shut the furnace off for a reason, and to check to see if 24 VAC is being maintained at the W terminal, which proves that the thermostat is remaining closed and not opening for some reason.

Do you have a manual thermostat or digital? Some thermostats have a heat anticipator adjustment in them that can cause the furnace to cycle on erratically if it's set improperly.
 
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Old 11-19-11, 08:56 AM
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It seems that I am chasing two different monsters here. I will test the voltage when I can reproduce the intermittent on/off issue, thanks for the suggestion. Another issue that I was able to track down is the "high limit open" error which occurs sometimes if I ask the heater to run for a longer period of time, in a situation when I raise the heat by say 3 degrees at the thermostat. The issue is that the limiter that I have is rated at 150 degrees, and I used a thermometer and it clearly shows that the temperature at the main vent/black rubber boot that you can pierce is exceeding 150 degrees tripping the sensor. I have very strong air flow out of my registers from what I can tell, so it does not seem like I have blockage in my vents. I am confused, either something is wrong or my limit sensor is rated too low?
 
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Old 11-19-11, 09:30 AM
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It is unlikely but possible that someone removed the limit switch installed by the manufacturer and put one in with too low of a shutoff point, although 150 is lower than I would normally expect to find.

Usually limit switches shut off for inadequate airflow across the heat exchanger caused by a plugged furnace filter, plugged air conditioner coil, too many warm air vents closed off or a cold air return that is covered over. Check those things first.

Getting good airflow out of your vents is a good indicator, but check EVERYTHING!
 
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Old 11-19-11, 09:43 AM
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The filter I just replaced this morning, the A/C coil was vacuumed/cleaned two months ago, all but 1 register are open in the house. The one I closed is because my heat runs so hot/strong that it was heating that particular room (directly above from the furnace) entirely too much. The heat exchanger is the only thing I haven't checked, I would have to pull a lot of things out to get to it. Like I said the flow is very strong. Is there any way to really know if 150 is simply too low for my system? I am going to wait until it gets colder tonight to try running it bypassing the sensor just to see how how it actually gets out of curiosity.
 
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Old 11-19-11, 09:46 AM
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There is a rating plate in the burner compartment of the furnace. Among other things, the heat rise specified by the manufacturer is listed there.

Post that heat rise and the temperature of the air being drawn into the furnace and the temperature of the air coming out of the furnace when the thermostat is set to 80 degrees and is thus calling for heat.

Use a good thermometer to measure those temperatures. No guessing allowed!

How was the AC coil cleaned, and why?

What was the condition of the filter you removed?
 
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Old 11-19-11, 02:31 PM
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The rise is specified at 35-65 degrees. It's currently 71 degrees at the thermostat (main level, it's a 3 level townhouse), I have the thermostat set at 80, using an infrared gun thermometer the air coming out of the registers in a room above the heater is about 135 degrees. The temperature at the rubber boot on the unit itself is reading 144, admittedly I'm using a kitchen thermometer at the moment. When I saw temperatures of 158 earlier today I was using a digital thermometer that a buddy had on him at the time (probably much more accurate than my kitchen one), it was warmer in the house as well as the unit itself has been running all day. Prior to this test I just ran I had the unit off while I was away for 5 hours. Bottom line is it's definitely bumping up against 150 degrees, and sometimes exceeding it by about 10 degrees perhaps. Honestly I am not so much concerned about this, I have no issues with it tripping from time to time and letting the unit cool off, I am more worried to see if the issue with the burners going out sporadically that I saw this morning comes back. The filter was fairly clean when I replaced it, I am religious about changing it every 3 months.

The AC coil was cleaned by a professional, my AC wasn't performing all that well during the hot summer so the freon was brought back up to spec along with cleaning the coil as well and the unit outside of the house.
 
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Old 11-19-11, 04:13 PM
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You aren't doing the test for heat rise accurately. You need to have the furnace turned way up so the burners will presumably remain on continuously, and do the test after the air from the furnace gets as hot as it will under that condition.

You need to measure the air temperature as it goes in the return air vent with a good quality mercury thermometer, and the air temperature at a warm air outlet as well. The difference in heat rise is the temperature rise.

From the temperatures you give it appears that the temperature is above the rated heat rise, which is bad for the heat exchangers and operation of the furnace. It implies that the fan speed is too low, the furnace is too big, the duct system too small or something is plugged up.

How was the AC coil cleaned? Did you observe it being cleaned?

Based on the information you provide, I would say you have a problem that needs to be analyzed by a GOOD furnace repairman who has the skill and weill take the time to measure the static pressure at the furnace and determine what the cause of the heat rise problem may be.
 
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