Intermittent igniting

Problems related to residential installations.

Intermittent igniting

Postby madmaxhvac » Sun Oct 27, 2013 8:27 pm

I have an interesting problem that is proving difficult to diagnose. Carrier 8000 Weathermaker 58WAV075, problems with intermittent igniting. Every so often it fails to ignite. When it does fail, it goes thru usual process, ignitor glows but valve does not open. No flame, then code 34 "ignition proving" error. Eventual code 14 lockout. If wait, turn off main power and retry it will often work again for some time a week or more. I've done the following with no success - cleaned flame sensor, cleaned draft safeguard switch, cleaned pressure switch, pressed reset switches on sensor that have them, and tested for 24v where it is supposed to be present. Then, since I have an identical twin furnace, one by one I switched out the controller and all sensors. Confirming each time that it does not fix the problem, and does not create the problem in the twin furnace. All I have left to test is the gas valve. I'm beginning to suspect this is the problem. Is there something in the valve that can stick or cause an intermittent problem such as this?
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- Intermittent igniting

Postby Freon » Tue Oct 29, 2013 3:15 pm

You say the valve does not open... does that mean you are able to observe the system when it doesn't light? If so, try and measure the voltage at the gas valve to be sure there's 24 volts at the valve when the call for gas valve open occurs. Usually you can hear the 'click' of a gas valve solenoid.

Also check all wiring to the furnace and to the gas valve. If it's a "Smartvalve" then there is a good chance it's the problem.
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- Intermittent igniting

Postby madmaxhvac » Wed Oct 30, 2013 5:29 pm

Thank you so much for the reply. I will try this. Yes to be more clear, when it doesn't work I can observe the valve and it tries to work. There is a click but it fails to send gas. I can tell there is no smell at all, valve doesn't open. and of course 3 tries and you're out! I find that often turning off the main switch gets it to reset and it works again for a while. Pretty sure I will confirm there is voltage there. If its a fault, is that a complete valve replacement or does one replace a solenoid or relay or something on the valve? I really appreciate the advice. I'm not familiar with gas valves and their repair.
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- Intermittent igniting

Postby Freon » Thu Oct 31, 2013 3:46 pm

Since the gas valve does work, albeit intermittently, the solenoid should be ok. The solenoid is just an electromagnet and if it were bad there would be an open circuit in the coil and no clicking whatsoever.

Verify the 24 volts AC is getting to the valve. It's possible there may be low voltage but since you hear the click of the valve, I doubt low voltage. Post the make and model of the valve and we'll go from there.
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- Intermittent igniting

Postby madmaxhvac » Sat Nov 02, 2013 4:43 pm

I confirm there is definitely 24 v at the valve, and a click every time. When it works and ignites the voltage remains, and of course if after the click it doesn't open, it doesn't light and the voltage drops to zero. For the gas valve there are the following nubmers 36E98 202 - EF32CW191A. From an internet search I think that might be a White Rodgers Gas Valve. Replace the valve ? Do they sometimes fail like this?
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- Intermittent igniting

Postby Freon » Mon Nov 04, 2013 6:04 pm

Good research. Now for more details.

This problem is complex because it's intermittent. You know the 24 volts and click happen at the gas valve when the furnace works. The real question -

When you measure 24 volts and hear the click AND the furnace does not work, does the 24 volts disappear immediately or is the 24 volts present all the time the furnace tries to light?

Here is the logic. If the gas valve voltage is present and you heard the click, then gas should be flowing into the burners. Why don't the burners ignite? Knowing the gas flows into the burners even when there is no ignition is important.

The gas valve could be working fine and there's a problem with the location of the hot surface ignitor(HSI). Or the HSI is operating intermittently... how old is it?

I want to make sure there's not an easier/simpler/less expensive solution before making you replace a good gas valve.
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- Intermittent igniting

Postby madmaxhvac » Tue Nov 05, 2013 1:53 am

Thanks. HSI is newish and glows well. The click is the same when it works or doesn't work, and voltage is there. It's like the valve is stuck. One issue I face is that the furnace can work fine for days without a problem so that makes it difficult to catch at that critical moment. I usually find it shut down with code 34, or 14 if it shuts off enough times. When I have been there to catch it and measure it, the voltage remained but not for long. And there is never any gas smell. Last night I read somewhere about these particular valves sticking. So I tried something after the first failure to ignite - during the second attempt to light I tapped the valve in a few places with a small mallet. Can't be certain this was the reason, but while tapping the valve, it decided to open and it lit. I could try repeating this test to be sure.
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- Intermittent igniting

Postby Freon » Tue Nov 05, 2013 2:37 pm

You are one step ahead of me. I was going to suggest tapping the valve when it seemed to not open. Excellent idea!

I would do a few more 'taps' with the mallet or wooden handle of a hammer when the gas valve appears to be stuck. If you find the valve consistently opens after the taps, I think you have logically found the problem.

Possibly there is a way to fix a sticky valve but I don't know with that specific valve. It is easy to replace. Be sure to turn OFF the power to the furnace before playing with the wiring. Also, label each wire to the valve (take a picture with a camera) so it's easy to reconnect. Good work!!
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- Intermittent igniting

Postby madmaxhvac » Tue Nov 05, 2013 2:41 pm

Thanks will do. If replacement is needed, I will call a professional.
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- Intermittent igniting

Postby madmaxhvac » Tue Nov 19, 2013 8:44 pm

Thought I'd report. I had the valve replaced, working perfectly since. Thanks again.
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