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I have a Burnham NG boiler, gotta be at least 25 years old. Never had a lick of trouble with it. It has an intermittent pilot light. It's conventionally vented into the chimney, no power vent. The controls are Honeywell. About a week ago I heard the burner stutter several times. Then yesterday when I was working nearby it did it again. The burner would stop firing, the ignition would fire almost immediately, and the burner would come back on, all the while the pump was running. It did it a couple of times.
I got inside it and removed the pilot assembly. It looks fine, and the pilot light orifice looks clear. The ignition and ground wires look fine, too. I was hoping something easy would be the source of the issue, but that doesn't seem to be the case. I think I'm left with the gas valve or ignition module being the root cause here but wanted to ask the brain trust for help in diagnosing what the problem might be. Of course Winter is coming. I heat mostly with wood but I go skiing for a week at a time and then the boiler has to work. Thanks in advance.
John
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11-11-2017, 11:31 AM
(This post was last modified: 11-11-2017, 11:33 AM by AUswimKC.)
Not familiar with boilers. I have a NG furnace. Mine would do the same thing. Inside there is something on the ignition valve that ensures that there is fire when the gas is flowing (ensures there isn't a gas leak). If it doesn't fire up it shutters and shuts the gas down. This part can get dirty and requires a quick scrub with steel wool the clean it. When dirty it doesn't sense the flame even when it's there. I have seen the same thing similar to what you describe when it was dirty. I would hear the gas flow loudly, and after a few seconds it would shut down. It would try 3-4 times and then shut itself down completely for a few minutes.
No idea if a boiler is similar, but maybe?
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Does it have a photocell or thermocouple to sense ignition???
Al
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Get me a model number for the ignition control and gas valve.
Blackhat
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(11-11-2017, 02:50 PM)blackhat Wrote: Get me a model number for the ignition control and gas valve.
Ignition Control Module = S86H
Gas Valve = VR8440
Pilot could be Q345, Q346, or Q348
I have to check if I have an ammeter that will go down into the microamps range, as I see that's how you verify if the Pilot is putting out enough current. Whenever I worked with thermocouples in the lab we were looking at millivolts not amps, so this seems strange to me.
Thanks,
John
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That control uses flame rectification to prove the presence of a pilot flame. Essentially, the pilot flame will rectify to DC, and conduct an extremely small amount of current between the electrode and ground. The control senses that DC current flow and allows the main gas valve to remain open.
The electrode and pilot shroud can be cleaned with a small wire brush and 600 grit sandpaper. It can also be sprayed with electric contact cleaner while it is removed. Don't spray it while it's installed or running. The newest versions include a small led that will blink a flame signal code. Do not attempt to measure the flame signal directly from the electrode. The spark voltage could destroy your meter. The control manual has a procedure for measuring flame strength.
Blackhat
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Keep in mind that the junction between the pilot burner and the other components are part of the electrical path for that flame signal and need to be clean and tight.
Anything that disrupts the stability of the pilot flame can cause a signal interruption or degradation. Drafts in the burner area or a pilot flame that is drawn off by a main burner can give the same result.
Blackhat
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(11-11-2017, 05:33 PM)blackhat Wrote: Keep in mind that the junction between the pilot burner and the other components are part of the electrical path for that flame signal and need to be clean and tight.
Anything that disrupts the stability of the pilot flame can cause a signal interruption or degradation. Drafts in the burner area or a pilot flame that is drawn off by a main burner can give the same result.
Thanks. I'll try cleaning the pilot electrode. I found the procedure for checking the electrode amperage so I may try checking that if I have an appropriate meter. I heard it misfire a couple of times this afternoon so the problem is still there - no surprise, really.
John
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(11-11-2017, 10:39 AM)jteneyck Wrote: I have a Burnham NG boiler, gotta be at least 25 years old. Never had a lick of trouble with it. It has an intermittent pilot light. It's conventionally vented into the chimney, no power vent. The controls are Honeywell. About a week ago I heard the burner stutter several times. Then yesterday when I was working nearby it did it again. The burner would stop firing, the ignition would fire almost immediately, and the burner would come back on, all the while the pump was running. It did it a couple of times.
I got inside it and removed the pilot assembly. It looks fine, and the pilot light orifice looks clear. The ignition and ground wires look fine, too. I was hoping something easy would be the source of the issue, but that doesn't seem to be the case. I think I'm left with the gas valve or ignition module being the root cause here but wanted to ask the brain trust for help in diagnosing what the problem might be. Of course Winter is coming. I heat mostly with wood but I go skiing for a week at a time and then the boiler has to work. Thanks in advance.
John
Did you check the vent to see if there was any obstruction? I don't know a thing about boilers but on a furnace it causes problems
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I cleaned the pilot sensor with 600 grit and haven't noticed any problems since. It hasn't run a lot, however, so only time will tell if that was the root of the problem. There was only a very minor amount of whitish accumulation on it, could have been oxidation or condensates from the NG, hardly more than a nano layer thick. Hard to imagine that could have caused the problem, but so far so good.
The flue is drawing fine but I'll have to get up on the roof and look down the chimney to verify all is OK. Maybe later today.
John
