25VAC to gas valve, no flame

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Old 11-30-14, 09:42 AM
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25VAC to gas valve, no flame

Hi, I have been doing some reading here and doing a bit of basic diagnosis on my attic-located Coleman gas furnace (house was built in 2000), the unit was installed then. Over the past week or two I've had intermittent issues where the system will shut off and flash the red (there is only 1 LED on my circuit board) LED 7 times. The chart on the panel says: "SEVEN FLASHES means IGNITION LOCKOUT DUE TO RETRIES".

The first thing I did was clean the flame rod. (Plus I think if the flame rod was the issue, I would at least get a flame in the first place).

When I issue a call for heat via the thermostat downstairs:

1) The inducer switches on, inducer fan appears to spin/blow well.

2) Hot surface igniter glows brightly

3) Sometimes the flame will come on only to go out 10-15 minutes later, while other times the flame won't come on at all. The igniter will glow 3 times and then the system will stop trying and will then light the LED 7 times to tell me "ignition lockout due to retries"

I measured AC voltage to the transformer: 121VAC.

I carefully pulled off both brown wires off of the Gas Valve spade terminals and put the leads of my multimeter in the ends of the wires at the connectors (female spade style) I observed 25 Volts AC when after the hot surface igniter reached peak brightness.

This tells me that I'm getting power to the valve and it is not opening to allow gas to the burners (Unless power to the gas valve can only be checked by back-probing the electrical connectors while they are connected to the valve). So I think I have a Gas Valve problem or an intermittent gas supply problem. I do not have any other gas appliances in the house other than my water heater so it's not like I can check my cooking stove and say 'hey - it is also intermittent here at the gas stove'. I would think that if I had a gas supply problem then because I have a gas water heater, I would expect to not always get hot water from my taps and showers throughout the house, however I have not had any issues with receiving hot water from any taps or showers during normal usage (4 shower usages per day around thanksgiving - with family here in town).

I don't have back-probing pins available today to try to check for 24 Volts AC while the connectors are plugged into the gas valve, but like I said above, I wouldn't think that should make a difference vs. checking for 24VAC with the leads unplugged from the gas valve so I can access the metal contacts in the female spade connector with my multimeter probes.



Any suggestions on what I should check next so I can get this heating issue fixed? Thanks in advance
 
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Old 11-30-14, 10:41 AM
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If you can get us the model number of the furnace we can see what gas valve you have.
 

Last edited by skaggsje; 11-30-14 at 10:42 AM. Reason: correction
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Old 11-30-14, 10:42 AM
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I wouldn't think that should make a difference vs. checking for 24VAC with the leads unplugged from the gas valve
You must check for 24vac to the gas valve with the valve wires connected. If you are worried about a flame while testing.... shut off the gas. The load of the valve will affect your test results.... that's why it needs to be connected.
 
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Old 11-30-14, 10:58 AM
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Where would the model number be listed on my Coleman? I looked on the removable front access panel and on the sticker that has the wiring diagram/diagnostic LED fault definitions - but I can't find it. It's also not on the Energy-Guide efficiency sticker on the front of the access panel.
 

Last edited by PJmax; 11-30-14 at 11:00 AM. Reason: removed board added link
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Old 11-30-14, 11:00 AM
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If you take the front service cover off.... the ID plate should be on the side of the cabinet near the burner area.
 
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Old 11-30-14, 11:06 AM
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Ok, I issued another call for heat from the thermostat. And this time on the 3rd lighting of the hot surface igniter, the flame lit. Not that it means my issue is resolved because as I had mentioned sometimes it will run for a while (a few hours sometimes, sometimes only 10mins, sometimes a flame won't even light even after 3 hot surface igniter attempts. However this time it did light and has been running and producing heat throughout the house for 50 minutes so far (I am timing it).

While it has been running I was able to backprobe the brown wires going to the gas valve - but instead of doing it at the valve itself (can't fit the probes of my multimeter wires into the back of the terminals plastic sheathing) I checked it at the control board at the large natural colored electrical connector. The wires are easily backprobed there. While it is running I am seeing 25VAC (which is expected because it is running successfully right now).

Going forward I will check it like this with all of the wires connected as you have suggested PJMaxx. I will continue to monitor. Keep the advice/tips coming guys, it is much appreciated. Let's see how long it runs for this time.
 
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Old 11-30-14, 11:11 AM
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Sorry I missed that, I had to lean down and look upward to see those stickers, here is the info:

MODEL NO. G8C05012MUB11A
 

Last edited by PJmax; 11-30-14 at 11:17 AM. Reason: removed board added link
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Old 11-30-14, 11:19 AM
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You have an intermittent problem.

It's very important to check every push on terminal for tightness and no corrosion. Make sure all the metal screws in the area of the control board are tight. Make sure the control board is well grounded. Go over every connection.... sometimes just disconnecting and reconnecting them is all it takes.
 
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Old 12-06-14, 10:46 PM
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Question

Ok, latest update: Today the system didn't fire up properly like it did back on my last post on the 30th (during that day the unit ran fine for hours once it lit up on the 3rd hot surface igniter lighting event). So I went back up in the attic and checked the system again.

Everything seems to work fine up until the gas valve needs to allow gas to flow. I have 24 VAC coming out of the step down transformer. With everything plugged in, I put my multimeter's leads into the two wires that are connected to the gas valve (by backprobing the female spade connectors). To switch it on, I jumped the red and white wire screw points on the control board. At around the moment when the hot surface igniter is at it's brightest (and at around the same time I hear a relay clicking for the gas valve) I get ~.3VAC. It only lasts for about a second and then goes back to zero Volts AC. I tested it again a few minutes later using the same method and this time on the 2nd and 3rd HSI events I got a brief 24VAC and the flame lit, however the 24VAC lasted only about a second or two and when it went back to ~0.3VAC/0VAC the flame naturally went out.

However, if I disconnect the leads from the gas valve and stick the probes into the spades on the ends of the wires - I see 24VAC at the point when the HSI is hottest. So it's like when the circuit is complete, maybe something is happening in my gas valve which doesn't allow 24VAC, or only briefly allows it for a moment, hence the brief 1-2 second flame. Thoughts? Thanks in advance!
 
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Old 12-06-14, 11:00 PM
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It's not the gas valve. It's more likely a defective relay on the control board. That why I had asked you to check it with the valve connected. The relay is dirty/corroded and will pass 24v as long as there is no load. Once the valve is reconnected.... the resistance is too high on the relay contacts to sustain the 24vac.

If you tap on the relay slightly with the handle end of a screwdriver..... it'll probably start to work again.
 
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Old 12-06-14, 11:09 PM
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Ok, that makes sense. Is it possible to replace just the defective relay on the control board? And I thought I saw some relays on the board, but how would I know which one to tap on (that may be a stupid question). What information do I need to get off of the board/relay to order the proper parts? I know a few guys at work who are pretty handy with a soldering iron, so if I needed to remove the control board and take it in to work I could do that. (I would label/take a photo of all of the wires going to the board). For what it's worth, I also have Grainger store nearby so I could probably get the parts I need pretty quickly (once I find out which ones I need that is)...
 
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Old 12-06-14, 11:21 PM
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The board is not considered repairable although I do repair them. Can you post the board part #.
 
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Old 12-06-14, 11:37 PM
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1Source P/N 031-01267-001A
 
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Old 12-07-14, 10:19 PM
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Hi, this was the part number that I was thinking of ordering: 331-03010-000 which is said to be the updated part number for my 031-01267-001A. Specifically, I was going to order one of the two below ebay item numbers:

381058702203

141432169574

Let me know what you think, thanks again for your time and expertise!
 
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Old 12-07-14, 11:27 PM
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It's very hard for me to keep up with retrofits and updated boards. Make sure the retrofit board lists the board you are replacing.
 
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Old 01-02-15, 07:49 PM
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I thought I would pop back in here to let you folks know that the issue was resolved. I have had a properly working furnace since a few days after my last post on here. Thank you to all who chimed in, but especially a big thanks to PJmax! I can see why you are a moderator, you really know your stuff and helped me out every step of the way:

It was indeed the furnace control board, (it must have been a relay on the control board as you had surmised), I bought and installed a new board and the system has been working properly since then. My family is happy and warm, Happy New Year to you and yours!
 
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Old 01-02-15, 10:18 PM
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Thank you very much for your praise and letting us know that your problem has been resolved.
 
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