Pilot Light Won't Stay Lit

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  #1  
Old 11-11-08, 09:03 AM
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Pilot Light Won't Stay Lit

We moved into a house with a 10 year old (or so) Peerless gas boiler for a baseboard hot water system. The pilot and boiler weren't lighting, so we had a plumber come out, and he changed the thermocoupler. Since that didn't solve the problem, he then replaced the gas valve. This seemed to do the trick for a couple weeks, but then the pilot went out again. I re-lit it a few times, but then it kept working with no issues for another week or so.

This morning, the pilot was out again. I went down to the basement and re-lit it, the system powered up and the burners were running as normal, but it stayed on for only about 5-10 minutes. After re-lighting again, it stayed on for another 5-10 minutes.

After it went out the second time, I tried my best to clear the pilot orifice with a bread tie to knock off any ash or debris (not sure how successful I was since the angle was difficult since I kept everything in place).

I also checked the placement of the thermocouple, and it appears to be in the flame, which is mostly blue with a bit of orange on the outside-left. The flame looks to be about an inch wide, so it definitely seems big enough.

After clearing the pilot orifice, I re-lit the pilot. The burners immediately lit and the system ran. However, this first "test" run lasted only 11 minutes until the pilot went out again. Since I was standing right there, I tried to re-light the pilot right away, but it wouldn't light until the third try (presumably until it cooled down?). When the pilot re-lit and I turned the switch, the burners, once again, kicked on.

The second "test" lasted only 8 1/2 minutes until the pilot light went out.

[Edited to add: For what it's worth, I re-lit the pilot but kept the boiler off. So far, the pilot has stayed lit for 30 minutes and counting. I'll update my post to let you know whether the pilot is staying on with the system turned off, which might help diagnose where the problem lies.]

I have a call in to the gas company to check on my input pressure, but we have had no problems at all with our gas-powered hot water heater, which is only 6 feet away from the boiler.

Can anyone recommend a possible solution? Any ideas on what is causing the pilot to continuously shut itself off? Improper or blocked venting? Not enough replacement combustion air?

Many, many thanks in advance!

BenderHeel
 

Last edited by BenderHeel; 11-11-08 at 09:45 AM. Reason: Update
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  #2  
Old 11-11-08, 03:39 PM
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Quick addition: The pilot light stayd lit for almost 5 hours this afternoon with the system off. I turned the heating system back on, and the pilot lit the burners, which stayed on for only 6.5 minutes, at which time the pilot and the burner shut off. There was the click of the gas valve closing when it shut down. The thermostat is set at 67, but the temp is only 64, plus that wouldn't explain why the pilot itself is going out and not just the burner.
 
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Old 11-11-08, 04:05 PM
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I'm going to stick my neck out: it must be the gas valve. If it were the thermocouple (again), then the pilot should have gone off with the gas valve off.

Here is one other theory. When your burner comes on, does the pilot stay the same size? If not, maybe you need to raise the pilot setting?
Doug
 
  #4  
Old 11-11-08, 04:30 PM
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In addition to the thermocouple, our plumber replaced the old Honeywell gas valve with a new one only about a month ago. So you think that new valve might be defective or not the correct one for the system?

The pilot flame looks to be the same size once the burners kick on.

I'm just at a loss as to why both the burner AND pilot light would kick off intermittently and no where close to what the thermostat is set for (that is, it kicks off even if the temp is 65 and the thermostat is set for 70).
 
  #5  
Old 11-11-08, 05:27 PM
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Pilot Problem

Does the pilot flame envelope at least the top 1/3 of the thermocouple while the main burner is on?
 
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Old 11-11-08, 05:34 PM
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Originally Posted by Grady View Post
Does the pilot flame envelope at least the top 1/3 of the thermocouple while the main burner is on?
Yes, the thermocouple is in the pilot flame about that far, and it gets red-hot. I doubt that the problem is with the thermocouple since the pilot remained on for 5 hours while the system itself was turned off. And the pilot flame appears to remain the same size while the burners are on. Until, of course, both the burners and pilot go out about 5-10 minutes later.
 
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Old 11-11-08, 05:50 PM
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Might possibly be a venting issue........have you had your chimney checked? Has anyone looked to see if the boiler is plugged?
 
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Old 11-11-08, 05:52 PM
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Pilot

With what you've said, I would have to suspect either the gas valve or most likely the thermocouple. The easy thing is to replace the thermocouple but I hate replacing parts I can't prove to be problematic. There is an adaptor which is made to allow you to test the thermocouple voltage while the thermocouple is in the system. As far as I know, this is the only way to know for sure.
 
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Old 11-11-08, 05:58 PM
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Vent

Good thought, Poorplmbr.
Would a blocked vent switch or other limit, such as a rollout switch, kill the pilot? I thought they were normally wired just to the main valve.
 
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Old 11-11-08, 06:15 PM
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True, Grady, that those safeties are wired to the gas valve ,but a plugged boiler will snuff out the main burners as well as the pilot
 
  #11  
Old 11-11-08, 06:17 PM
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Originally Posted by poorplmbr View Post
Might possibly be a venting issue........have you had your chimney checked? Has anyone looked to see if the boiler is plugged?
I haven't had the chimney checked; the most that I could do was to open the vent (by pulling out the bottom cap) and I could feel an upward draft, so I figured that it was okay. But I have thought that it might be a venting issue.

Where would I find a vent switch to check that? Or a rollout switch?

What do you mean by the boiler being "plugged"? I haven't come across that issue in my internet searching/diagnosis.
 
  #12  
Old 11-11-08, 06:46 PM
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Originally Posted by poorplmbr View Post
True, Grady, that those safeties are wired to the gas valve ,but a plugged boiler will snuff out the main burners as well as the pilot
What is a "plugged boiler"? And how does one de-plug a boiler??
 
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Old 11-11-08, 06:53 PM
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Plugged boiler

Take the vent pipe off the top of the boiler. On most boilers you can look down thru the opening at the passages the heat must take to get out of the boiler & to the exhaust. There shoud be what looks like hundreds of grease fitting sized pins. Between them should be clean, not plugged with rust, soot, etc.
 
  #14  
Old 11-12-08, 06:15 AM
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Gas Meter

My pilot light was also giving problems, but only certain times of the day. Well, to make a long story short my gas meter was freezing up at night and during late morning when the sun was out the gas flow was fine. The gas company replace the meter when they came out early in the morning and noticed I had no gas flow.
 
  #15  
Old 11-12-08, 08:10 AM
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Without doing anything else to it, the system is working fine today. When the burners go out, the pilot stays lit.

I had an HVAC guy out today, and he thinks that the problem might be a draft caused when the burners go out, sucking out the pilot light as well. We don't have a chimney cap and our terra cotta chimney liner has seen better days, so he thinks that the pressure created is sucking the pilot out when the burner goes out. I'm going to have the chimney capped first and see where that takes us.
 
  #16  
Old 11-12-08, 08:37 AM
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Can you watch the pilot? If you have a helper have them turn down the thermostat after the boiler has run for a few minutes. See if that takes out the pilot. If no helper then will need to watch until the call for heat has ended.

Same as Grady stated I too don't like doing things unless it is proven. Otherwise the dollars go in lots of circles.

Al.
 
  #17  
Old 12-12-08, 01:12 PM
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Okay I'm back....and so is the lack of heat in my house!

After our last go-round, our plumber recommended that we get a chimney cap since he thought that our problem -- the pilot light going out when the burners cycle off -- was caused by a large draft going up the chimney associated with the burners kicking off. So we got the chimney capped and cleaned, and no problems with the heat for the past month...until I got home from work yesterday.

Same problem: the pilot is out. I relight it. System kicks on because the room temp is below the set temp. After approximately 5 minutes, the boiler wants to cycle off, and when the burners go out, so does the pilot. Thus, no more cycling because no more pilot. The circulator continues to run.

I've called the plumber back, but I'm at my wits end. This is our second plumber, and neither seem to be able to properly diagnose this problem. (The first said it was a drop in gas pressure associated with the provider. But it doesn't affect the hot water heater, which is 5 feet away, and plumber #2 says that plumber #1 is wrong.) I can't continue to dump more money into different issues since we already have dumped way too much already (new thermocouple, new gas valve, chimeny sweep and cap).

Does anyone have any guesses as to why the pilot would start to go out when the burners cycle off? And why the heck would it do it for a day or so and then not do it for a month? It seems like it's happening almost once every 4 weeks. HELP!
 
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