intermittant code #34 and then #14(ignition lockout)

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Old 11-25-09, 07:49 AM
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intermittant code #34 and then #14(ignition lockout)

I have an eighteen year old Payne furnace, model 398AAV, that runs from ten minutes to two three days before quitting. The pressure switch has been replaced and the lines checked for blockage. The flame sensor has been replaced. When the flame ignites, it looks good and there doesn't appear to be any issues with flame carryover. The hot surface ignitor works fine. The technician suggested that perhaps the heat exchanger was cracked and he removed the blower to inspect the heat it. He said there was no sign of corrosion, but he couldn't see up into the exchanger. He recommends replacing the furnace due to its age.

Is there any possibility that the control circuit board be part of the problem, or when it fails, does it fail completely? Any insight/suggestions you can provide would be appreciated.
 
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Old 11-25-09, 09:09 AM
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Yes, the problem can be the circuit board failing to detect the burner flame.

You need to measure and report the DC microamps flowing through the flame sensor back to the circuit board while the burner are lit.

Also, measure the AC volts on the wire going to the flame sensor while the thermostat is calling for heat.

Any competent repairman would have done that before replacing the flame sensor, so I don't think much of the guy who checked out the furnace for you.

Keep in mind we are talking microamps: 1000000 microamps= 1 amp.
 
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Old 11-25-09, 12:10 PM
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Thanks much for the input. I'm going to borrow a friend's meter and check it out. My $10 Craftsman digital multimeter doesn't quite cut it!
 
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Old 11-25-09, 03:45 PM
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Clean the flame sensor with some steel wool and verify that the control board is getting a good ground. Dirt can become lodged between the circuit board mounting bracket and the furnace chasis creating a poor ground connection on some models. (Models with a ground screw on the circuit board)

This is a pretty good article on the subject...
Flame Rectification
 
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Old 11-25-09, 07:56 PM
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Frankly, with those diagnostic codes I'd consider it a complete waste of time to have replaced the pressure switch. Those codes point rather directly a flame failure circuit problem or issue of some kind. Replacing the pressure switch in such a circumstance is dumb, dumb, dumb!
 
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Old 01-09-10, 09:50 AM
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Help! Similar problem.

My furnace works for a few hours or less then the code 34, (ignition proving failure) then the code 14 (ignition lockout).

It is a relatively new Payne PG8U. The weird thing is that we figured out that if we just turn the breaker off for 30 seconds and turn it back on, it starts working again (for a few hour or less, then code 34, then 14, turn it off, start the cycle again).

I see the igniter light up and it catches flame often, but then then it lights up, no flame, code 34.

Any thoughts? I thought that maybe it was the flame sensor, but I don't know where to find it to clean it.
 
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Old 01-09-10, 10:31 AM
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The flame sensor is a likely cause of the problem, and as an added bonus it's easy to clean, and should be cleaned annually anyway.


The flame sensor is typically on the opposite side of the furnace from the hot surface ignitor that glows white hot to light the gas.

It's a small rod that sticks up into the flames and has one wire coming off the bottom and going back to the circuit board/ignition module.

Take it out and clean it with a wire brush or some fine sandpaper. You don't need to cut into the metal--- you are just cleaning any invisible coating of oxides off of it.

Give that a try and see what happens.
 
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Old 01-10-10, 09:33 PM
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That seems to have done the trick! Thanks so much!
 
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