Furnace Ignition Failure

Problems related to residential installations.

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LookingSharp
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Furnace Ignition Failure

Post by LookingSharp » Sat Nov 29, 2014 2:58 pm

My furnace stopped working this morning. The board code is Ignition Failure. It looks like the initial blower is starting up, the ignitor starts up, and then when the main fan tries to start there is an odd noise. I captured a video and posted it to Youtube. The interesting part starts at 44 seconds.
*.*/watch?*

It looks like URLs don't post right. On Youtube if you search for 0V6aU3XHdjc then you can see the video.

Thanks.

Freon
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- Furnace Ignition Failure

Post by Freon » Sun Nov 30, 2014 2:23 pm

It looks like you have a normal burner ignition and the furnace runs as you'd expect until that noise. Is that correct?

Does the noise exactly coincide with the main blower starting?

Can you locate where the noise is coming from and what it might be? It almost sounds like the smaller blower (inducer) squirrel cage may be hitting something or it could be a relay chattering. The noise is the answer.

LookingSharp
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- Furnace Ignition Failure

Post by LookingSharp » Wed Dec 03, 2014 12:25 pm

So I had someone come out and diagnose it. The breeze inducer is working fine and not making the noise. It turned out to be the automatic gas valve. Here's another video, where tapping on the valve gets it to turn on - pkmQ4EetmdU

This was on a Saturday, and they couldn't get the part. We tapped on the valve during the day to get it to come on. By the evening it was coming on automatically all on its own. It's been 4 days, and it hasn't had a problem since.

Here are some questions -
1) They didn't measure the voltages on the valve. I've since talked to another furnace repair shop, and they thought he should have. Is it possible it isn't the valve, but is the controller?
2) It's been working for 4 days now. Should it still be replaced, or can these valves recover?

This is my furnace model number - G6RK-096C-16B

Thanks for the help,

dave

Freon
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- Furnace Ignition Failure

Post by Freon » Wed Dec 03, 2014 2:50 pm

The sound you hear is the gas valve solenoid chattering. The question is what's causing the chatter. You will want to check the voltage to the gas valve when it's operating normally. It should be constant at about 24 volts AC. If it starts to misbehave and chatter, you'll want to check the voltage at the gas valve again. If you see the voltage fluctuating you'll know the cause of the chatter. If it's a "smart valve" (post the valve make/model) you'll see a small printed circuit board on the valve. Those are known to be a problem. Since you bang the valve to get it to work, I doubt the problem is with the main furnace control board. But if you see voltage fluctuations they could be coming from the main control board or the valve PC board. It is also possible the solenoid coil is developing a short. Intermittent problems are the worst.

Also check the wiring to the valve. Banging the valve could fix a loose wire or a broken wire where the break is hidden by the plastic insulation. Until we know the true cause we'll not know if this valve is fixed permanently. There is no recovery other than repair or replacement.

LookingSharp
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- Furnace Ignition Failure

Post by LookingSharp » Wed Dec 10, 2014 4:20 am

I had the valve replaced. They measured the voltage on it, and it does seem low - around 20 volts. I had them replace the valve anyway, as that is how they diagnosed it when it was having a problem. We'll see what happens.

Freon
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- Furnace Ignition Failure

Post by Freon » Wed Dec 10, 2014 1:23 pm

I hope all goes well for you. If that 20 volt AC measurement is accurate, that is low voltage. A gas valve is only a simple solenoid with a counterbalancing spring. If the voltage is insufficient enough to make the magnet in the solenoid overpower the spring, the valve will not always work properly.

If you have a multimeter, I'd check the AC voltage at the transformer secondary when the furnace is not running. It should be 24 volts. Then check at the same location with the furnace running. If the voltage drops to 20 volts then either the transformer has problems or some part of the circuit board is drawing too much current.

LookingSharp
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- Furnace Ignition Failure

Post by LookingSharp » Fri Dec 12, 2014 11:52 am

Well, a few days later and no heat. They're coming back out later today. It is acting a little differently now - the indicator light is continuously flashing, which is labelled as false flame or gas valve shorted.

I don't know enough to say whether 20 volts is within tolerance, but they seemed to think so. Does that sound reasonable? While the measurement is supposed to be 24 volts, is 20 ok? Could it be that the voltage is ok and I just got a bad gas valve?

If it is either the transformer or the circuit board - which do you replace? Can they do any other test to determine which is bad? Both parts sound expensive - is it just a 50/50 crap shoot?

Freon
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- Furnace Ignition Failure

Post by Freon » Fri Dec 12, 2014 4:00 pm

The transformer is very easy and inexpensive to replace compared to the control board. It's important to know the AC voltage from the transformer where it connects to the control board. If it's 20 volts, that's too low, in my opinion, for reliable functioning of the gas valve. But there could be a bad component on the circuit board that's causing a higher than normal load on the transformer and causing the voltage drop.

If the furnace is old I'd start with the transformer. They're about $20 and easy to replace. It is a crap-shoot, you're right. So start with the least expensive and go from there. If these technicians are good, that can test the transformer. I hope you get an honest opinion... selling expensive parts is more profitable. I hate to by cynical but that's how all professions go... sadly. Good luck.

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