Can a (possibly) failing gas valve work intermittently?

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Old 01-19-13, 06:54 PM
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Can a (possibly) failing gas valve work intermittently?

I have been scouring this forum all night while trying to diagnose my issue. A lot of useful information and helpful people. Thanks in advance.

I have a:
Ruud Silhouette II
Model Number UGPH-10EAMER

That is at this moment working fine. However, for the past 3 hours I've been trying to figure it out a series of different malfunctions.
At first:
Inducer motor runs for 30 seconds
Igniter sparks up
No Flame at all.
Repeats over and over.
So I shut the power off for a while.

Later, turn the sytem back on:
Inducer motor runs for 30 seconds.
Igniter sparks.
Flame would catch in just the first "tunnel" to the heat exchanger.
or
Flame would catch across all burners and then shut off after a few seconds.
But in both instances would quickly shut off.

I know that if the flame catches yet shuts off it could be buildup on the flame sensor so I took out the steel wool and made sure it was clean.

During all these instances I would have 2 green lights on the board.

As I have been typing this the furnace seemed to properly finish an entire heating cycle properly. I don't know everything about HVAC but I'm pretty sure there aren't "Heater Genies" miraculously fixing this issue.

So could the gas valve work sometimes and be a symptom of a future failure? I sadly do not have a working multimeter so I cannot get voltage readings at the moment.

Update as I finish this post: System cycled on, flames lit for 3-5 seconds and then were gone. The blower is running as if it were heating. Then it cycles again and works fine. I believe it's gained self awareness and is toying with me now.

All hail the malevolent heater overlord!!
 
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Old 01-19-13, 07:29 PM
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Welcome to the forum,
I had the same problem in 2 different units. On one, it turned out to be the ground screw was loose, and sure enough as soon as it got tightened everything was fine. On the other unit, which was in its 1st year of service the condensation hose had not been installed and water was building up in the unit.

Hopefully, the experts will be here soon to tackle your problem.
 
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Old 01-19-13, 07:46 PM
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Probably not a DIY project.

Gas inlet presure, outlet pressure, vacuum at pressure switch, crossover condition, ground connections, flame rectification, & voltage to gas valve, should be checked.

Wouldn't be a bad idea to have the capacitor measured, blower amperage, heat rise and external static pressure checked and compared to furnace specs while you have a tech there.
 
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Old 01-20-13, 01:28 PM
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A manual on your furnace can be found and downloaded at:

http://www.acdirect.com/shop/images/..._448_Rev10.pdf


Unfortunately, it doesn't have some useful information like a circuit diagram for ther furnace and an explanation of what the diagnostic codes indicate.


<<Gas valves tend to be very reliable, so there is a high probability that the gas valve is fine and something else is causing the problem.

>>



You have a direct spark ignition furnace. This means that the main burner gas should be lit directly from the spark, which means that the main burner gas should switch on when the spark turns on.

If the flame sensing system doesn't verify that the burners lit properly within 3-5 seconds, the gas and spark would turn off and the ignition sequence would begin again. IS the spark shutting off when the burners don't light, and the ignition sequence beginning again?

Many of your comments are vague, not being specific about what is happening. Detail is important to diagnosing problems.

If the main burner gas isn't turning on when the spark does, I'd use a multimeter to measure the voltage being applied to the gas valve. When the spark turns on, you should be getting 24 VAC applied to the gas valve when the spark turns on. Check to see if that is happening.

It's far more likely that the circuit board is failing to turn on the voltage than that the votage is turned on and the gas valve isn;t opening, but guessing is no substitute for checking to see what is actually happening.
 
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Old 01-23-13, 07:44 AM
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Is your unit natural gas or gas from a tank (i.e. propane)?
 
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