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Old 01-09-2010, 06:16 PM   #1
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Losing burner flame and pilot flame


Hi there I have a COZY cf503c-h direct vent wall furnace. After running for a while (average 2-3 hours)the gas will completely shut off...no burner and no pilot. I've had 3 techs out to look at it 4 different times and the leave shrugging their shoulders. We can re light the pilot at anytime after it shuts down with out pushing any resets or making any adjustments. There was virtually no wind today when it happened so there wasn't wind blowing down the vent at all. We have replaced the thermocoupler twice and ajusted and cleaned the pilot oriface. A tech also took volt reading from the gas valve and thermocoupler and all seemed fine. I had to replace the gas valve in Dec of 07 but don't remember why. What is causing this to happen? This is in a rental unit and my tenants are getting frustated with no heat and people in and out all the time and I'm getting tired of paying techs to come out and shrug their shoulders. Can you help me?

Optional Information:
Make : Cozy
Model : cf503c-h

Already Tried:
2 thermocouplers adjusted pilot flame cleaned pilot orifice received normal voltage readings from gas valve and thermocoupler.

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Old 01-09-2010, 06:39 PM   #2
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Losing burner flame and pilot flame


Does this vent to a old style brick chimney or a dedicated b-vent metal chimney? There is a blocked flu switch that may be manual or automatic reset. Do you know if it is manual reset or not?

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Old 01-09-2010, 07:20 PM   #3
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Losing burner flame and pilot flame


Thanks for the reply John, it vents directly out wall that it is on. There is a manual limit switch near the bottom, that I never had to reset, and I have't had manually reset anything.
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Old 01-09-2010, 07:27 PM   #4
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Losing burner flame and pilot flame


On most wall furnaces that I have seen the limit is self resetting - not so say that your is or is not. Your wall furnace may be overheating and causing the limit to trip. Have the tech check manifold gas pressure - it may be overfueling. Also check to see that the heat exchanger is clean (exterior) for free air circulation
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Old 01-09-2010, 07:43 PM   #5
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Losing burner flame and pilot flame


The limit switch is a manual reset as well as the blocked flue switch. The heat exchanger is clean and no cracks on the room side that we could find. It has plenty of air flow around it. I have seen the red reset button on the limit switch and have never had to touch it. Even if that did trip would it shut down the pilot too? Could maybe the blocked flue switch be faulty to a point that it cuts off the gas valve but doesn't pot the reset?
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Old 01-09-2010, 07:55 PM   #6
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Losing burner flame and pilot flame


Where the thermocouple attaches to the gas valve is there two wires making a connection? Most the time the wire are red in color.
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Old 01-09-2010, 08:10 PM   #7
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Losing burner flame and pilot flame


I'm trying to remember now, since this is in an apartment, but I think there were some black wires there, and I seen the tech wiggling them to make sure they were tight.
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Old 01-09-2010, 08:15 PM   #8
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Losing burner flame and pilot flame


If there is wires off at where the T-couple connects then these wires go to the limits. When a limit trips then it opens a circuit and shuts off the main burner and pilot.

I have in the past taken the limits out of the circuit by jumping the wires and operate the heater. DO NOT LEAVE IT THIS WAY. If it still acts up replace the gas valve if it doesn't then check wiring and limits
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Old 01-09-2010, 08:26 PM   #9
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Losing burner flame and pilot flame


That makes sense and I'll try that tomorrow...2 concerns I have with that though

1. If the limit switch cuts would that also cut the pilot? I expressed concern about a bad limit switch to all three techs and they said that it wouldn't cut the pilot. I don't think they have worked on many units like this though, mostly standard home furnaces. One tech tested continuity and said it was good, but of course it would be if was cooled off by then..but....

2. since both limits have manual resets wouldn't they have popped if they were cutting off the gas valve?
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Old 01-09-2010, 08:42 PM   #10
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Losing burner flame and pilot flame


Quote:
Originally Posted by papashaq View Post
That makes sense and I'll try that tomorrow...2 concerns I have with that though

1. If the limit switch cuts would that also cut the pilot? I expressed concern about a bad limit switch to all three techs and they said that it wouldn't cut the pilot. I don't think they have worked on many units like this though, mostly standard home furnaces. One tech tested continuity and said it was good, but of course it would be if was cooled off by then..but....

2. since both limits have manual resets wouldn't they have popped if they were cutting off the gas valve?

Q1 If the wires are connected to the t-couple then yes it will shut off the pilot. Most the time on this style of heater if a limit trips it shuts off the pilot and most Cozy heater operate this way. (Removes ignition sorce and main burner operation)

Q2 Double check the limits (Not to say it is or isn't / I'm not there) but I have never seen a manual reset limit on a Cozy heater. I think you will find that it is self resetting. I'm betting it is the top limit
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Old 01-09-2010, 08:55 PM   #11
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Losing burner flame and pilot flame


Ok thanks for the help. I see it's only about $16 to replace both limits so I'll try that and hope it's a bad limit, if not I have more problems then I want. Do you know what the manifold pressure should be for this unit?
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Old 01-09-2010, 09:00 PM   #12
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Losing burner flame and pilot flame


In measuring gas pressure we use Inch of Water Colum (INWC) and not PSI. Manifold pressure should be 3.5 inwc.

I'm sure I'm off but 1 psi equals approx 27 inwc

You need a manometer to measure gas pressure
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Old 01-09-2010, 09:07 PM   #13
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Losing burner flame and pilot flame


If limits are opening.
Something is wrong. And probably NOT the limits.

If your gas pressure is too high, The heat exchanger can become hot enough, that when the stat stops calling for heat. And the gas valve shuts. The pilot flame is sucked/drawn from the pilot, and it goes out.

DON NOT bypass those limits.

Your not going to sit there for 3 hours to see what happens are you.
Its not safe to leave and say to the tenants tell me what happens.

You may have a bad wire connection.
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Old 01-09-2010, 09:14 PM   #14
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Losing burner flame and pilot flame


I was looking at the diagram again and I see there is an auxiliary limit switch. That is the one I was seeing with the manual reset button. What is the Auxiliary limit switch for?
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Old 01-09-2010, 09:31 PM   #15
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Losing burner flame and pilot flame


Thats for when the main limit fails to open.

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