Boiler spill switch keeps popping.
I have a Dunkirk Model PWB-5D electronic ignition boiler. This boiler was installed in 2000. The boiler heats our water in addition to heating the house in the winter. All year long the boiler comes on periodically to replenish our hot water supply.
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This is the third summer we have been in this house. This is the first really warm summer we have experienced.
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The day before the heat arrived, we installed a Unico system to cool the house.
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This summer, the spill out switch on the boiler started popping. According to the manual, flue blockage is the normal cause of the spill switch popping. Our HVAC contractor cannot find any blockage. Further, the problem seems to intermittent. This would seem to rule out any fixed blockage.
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After the spill switch is reset and the boiler fires, you can feel a very definite spill out.
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Just after we got the air conditioning in, we added to our house. This addition extended our 4/12 roof and raised the roofline 10 inches about 6 feet from the chimney.
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After we raised the roofline and the spill switch popping became noticeable, our HVAC contractor added 3 feet to our chimney. This has not solved the problem.
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Any ideas what’s causing this problem?
Replies
You have a negative pressure in the house. Do you have a combustion air duct? Whole house fan? Flue blockage is usually the last cause of a spill switch tripping.
We have a combustion air duct.
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We have an attic fan which runs most of the time. The attic is vented although perhaps not adequately.
Why negative pressure after 2 years when we apparently had none?
Any other work done, when the reno was done? New windows, weatherstripping? Try shutting the fan off for a while.
So far the addition has only been framed and weather sealed. No new windows or other changes affecting the tightness of the house or the boiler area.
Fan was formerly on continuously. Fan now on automatic. No spill switch pop since that change. Weather has been cloudy since then.
I'd investigate what is making the air come into the house via the chimney - normally it does the other way. Besides the whole-house fan, other likely culprits are bathroom fans, kitchen hoods, and other fan-like appliances that interact with the outdoors. It is also entirely possible that your renovation work has tightened up the house to the point where the makeup air is coming in via the chimney.
Here is how I would test the rig: Open a window, door, etc. from the outdoors to to the basement, also have at least one or two doors open upstairs, with the door inside the home to the basement closed. Does the heater light off OK? If so, makeup air is your most likely culprit. Next, test the rig with just a basement door open. What happens?
My guess is that the house is being evacuated by some means, be it infiltration + stack effect through the house, or a fan that is actively depressurizing it (more likely the latter). I would ensure that the boiler has a adequate, dedicated combustion-air supply and that it is clear of debris.
In my house, the combustion air intake is 4" in diameter and we have purposely sealed the utility room to be treated as part of the outdoors (i.e. external grade door, insulation, sealing, etc.) In some states, like MA, an atmospheric boiler would require by code a fan-assisted combustion-air intake whenever it is operated in spaces that do not feature a open-to-atmosphere intake.
If your boiler has neither a dedicated combustion air intake nor a fan-assist, you're in good (though dangerous) company. I recently visited a small basement with close to 1 million BTUs of heating appliances and no air intake. This kind of madness only maybe works until homes are insulated... but once infiltration isn't the norm but the exception, the stage is set for bad combustion, CO-generation, and possibly death.
The boiler has a dedicated 4” combustion air supply.
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I have checked the inlet to the air supply tube and it is clear. The outlet should be clear since nothing has changed. When I checked the air supply with the boiler going, there did not seem to be much air coming in through the supply tube. I will have that checked.
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The renovation did not tighten the house, it so far has loosened the house. The renovation has only so far gotten to framing and removal of the wall between the house and the addition. The addition is not in any way air tight. It is barely weather tight.
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It may be that the recently installed whole house air conditioning is the culprit. Although it does not remove any air from the house, the pull of the air return may be affecting the boiler. This is a high velocity air movement system. It may be pulling in air with much greater force than it is distributing air. The different in force is a result of the friction in the supply tubes.
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The solution may be to isolate the boiler room from the rest of the house and rely only on the dedicated combustion air supply. This change would minimize the effect of the attic fan and of the air conditioning air mover.
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It seems that one thing I really need to do is get a CO monitor. Then at least I and my wife will not die while we are figuring out this problem.
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The challenge is that the problem is very intermittent. Quite some time might be need before the cause of the problem is identified. For example, when it is not cooling, the A/C system moves much less air than when it is actually cooling. So the problem may occur only when the A/C system is running, the attic fan is running and the house is calling for hot water.
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But I will set up a test running all systems at full blast and see if that causes the switch to pop.
Well, I guess I am starting to scratch my head a bit here. Is the AC system running through the same space as the boiler? Are there any inlets into the AC somewhere in the same space as the boiler?As for CO monitors, your best bet is either the national comfort institute model (your HVAC contractor can order it) or the COExperts monitor. If your HVAC tech has any trouble, simply order the COExperts unit from aeromedix.com, the best price I have found on the web so far for single-digit quantities. Only these two monitors are worth buying, everything else being sold into the residential market is junk, IMHO.One other thing I'll ask is if ANY part of the house is taller than the chimney you're feeding into with the furnace. It is my understanding that homes where a part is higher than the chimney can have severe drafting issues.Going forward, you may consider switching to a sealed combustion, modulating, and condensing boiler like the Munchkin, Ultra, Vitodens, etc. as they pretty much completely erase the possibility of CO issues, drafting problems, and offer superior efficiency to boot. In the meantime, you can attempt to re-create the conditions that are causing spilling by a process of elimination where you run all appliances and see if they can cause the problem as a whole. Then start eliminating appliances until you have the single one or the combination thereof that causes negative draft in the basement.PS: CFM = cubic feet per minute, which is a measure of air volume.
>>As for CO monitors, your best bet is either the national comfort institute model (your HVAC contractor can order it) or the COExperts monitor. If your HVAC tech has any trouble, simply order the COExperts unit from aeromedix.com, the best price I have found on the web so far for single-digit quantities. Only these two monitors are worth buying, everything else being sold into the residential market is junk, IMHO.I have a few of the NCI monitors which I can sell for $125See http://www.nationalcomfortinstitute.com/members/products2.cfm?product_id=21&Cat=Consumer%20Products
for more info.
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All A/C return/supply orifices are in the ceiling of our ranch house. The boiler is in the basement. So there is plenty of separation between the two.
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We have an unusual roof design. Our house is sometimes referred to as the ‘pin wheel’ house. The chimney is at least 3 feet higher than any part of the roof.
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We here have these things called trees. The chimney is surrounded on 3 sides with tress 100 feet tall. These trees are at least 50 feet from the chimney. The spill problem started about 6 weeks ago. The trees were there when we bought this house 3 years ago. I understand the trees have been there since the boiler was installed in 2000.
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The boiler is only 5 years old. So we will try hard to solve the problem without replacing the boiler.
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My next step is to have the combustion air supply tubing checked. While the inlet is clear, we may have had hornets build a nest inside it.
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Thanks all. Your thoughts and suggestions have been most helpful.
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PS: I guess my HVAC contractor was right – I just would not understand what CFM means. I understand that cubic feet measures volume. But where does the ‘per minute’ come in? Or does CFM refer to velocity rather than volume - cubic feet of air at standard atmospheric pressure moved per minute?
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I must get out my physics books and study again Bernoulli’s Law of fluid dynamics.
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Here is an excerpt on misinterpretation of Bernoulli’s Law authored by Klaus Weltner of University Frankfurt: “Bernoulli's law and experiments attributed to it are fascinating. Unfortunately some of these experiments are explained erraneously, e.g.: the function of a vaporizer and the soaring of a ping-pong ball in a jet stream of a hair dryer can not be used as applications of Bernoulli's law. The static pressure in a free jet stream is equal to the static pressure in the environmental atmosphere regardless of the streaming velocity of the jet.” This probably makes more sense in German.
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Well, I guess I had best leave things like CFM in the hands of you HVAC professionals.
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I wish you a good cup of coffee this morning and a good laugh.
You're on the right track. I am sure that with the diligence that you and your HVAC contractor are putting in that you'll eventually figure out where the problem is. Like you, I doubt that it's environmental, and the high chimney should make for a good natural draft. I'd still go through the basement though and see if there are any penetrations to the spaces above where a lot of air could be escaping. Just foam them shut... fiberglass insulation does not stop air movement, BTW.As for CFM, it's a bit like kWh. You have a measure of an air volume (a cubic foot) and now simply add another measure (like per minute) to denote how much mass is being moved in a given time period. It's just like mass-flow for pumps (gallons per minute), energy flow for electricity (kilo Watts per hour), etc. For example, given how sensitive modern internal combustion engines are to changes in air pressure, temperature, humidity, etc., todays car engine management programs use Mass Air Flow (MAF) sensors to accurately set themselves up for clean combustion.
"As for CFM, it's a bit like kWh."Actually very differently.Although they both have a time at the end of they have very different meaning.CFM - cubic ft PER MINUTEkWh - number of kW used TOTALE OVER AN HOUR. kW is the rate of using energy.CF <=> GAL <=> kWh
CFM <=> GPM <=> kW
Bill, perhaps I'm dense but I do not seem to understand the hair-plitting going on here.
In its simplest form, a cubic foot is a measure of volume. When attached to a material like air, it can also denote a measure of mass. Attaching a measure of time can indicate a measure of mass flow over time, i.e. CFM, for example.
On the water side of the heating business, people usually think in terms of gallons because that is a common US unit of measure for a quantity of water. Gallons per minute or gallons per hour hence indicate how much mass a pump can move.
Similarly, a kW is a measure of work that take many forms, such as 3412 BTU/kW in a resistant heating application, so and so much torque / kW for a motor creating motion, etc. Attaching a measure of time simply allows for an easily-understood accounting of how much "work" has been performed.
As the later part of my last paragraph describes, I never tried to imply that a kWh = GPM = CFM as your post suggest, so I'm not sure where you're going with this. Cheers.
kW is the RATE at which energy is used (or flows as you describe it).And likewise CFM is a RATE measurement. The rate at which volume is being moved.kWh is a cumulative measurement or the TOTAL amount of energy.Likewise CF is a cumulative measurement or the TOTAL amount of air moved.
Bill, this is getting into semantics. I mean the same thing as you, perhaps you express it better, I don't want to fight about this, so you win. Time to buy yourself an ice cream. Cheers!
You have negative pressure in the boiler room at the times of the rollout on light off.
You need someone with a draft gauge and an open mind.
People training in the Carbon Monoxide Analysis Protocol now offered through the National Comfort Institute are probably your best bet.
Were there any changes made to the boiler room? Was it enclosed?
Is there sufficient combustion air? (50 cubic feet per 1000 btu in the boiler room and space it's open to?) I doubt this is it, because that usually doesn't't cause rollout at light - off, but it should be checked.
Do the A/C returns pull air from the boiler room, or near the boiler room? That could create the negative pressure which is cause.
Has the boiler been serviced recently? The ignitor replaced or moved?
It can take a lot of time to find the culprit.
And there can be multiple causes; don't' stop when you've found one; keep looking for other contributing factors and fix them all.
I have a very fine licensed, certified HVAC contractor. He is a man with a very open mind. I worked beside him installing the A/C system. I did the electrical and drains while he did the air handling and refrigerant.
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Don’t know whether he has a draft gage. I once asked him if he had a CFM meter (whatever CFM is) and he said “No’. (CFM is one of those technical terms understood only by members of the profession. I wanted to check the CFM (whatever CFM is) from one of the A/C outlets that is noisy.)
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The only change in the boiler room was part of its outside wall was removed to give access to the crawl space of the addition. Also the standalone dehumidifier in the boiler room was upgraded.
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The A/C return is in the ceiling of the first floor of this one floor house. The boiler room is in the basement.
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The boiler has been inspected within the last week, but not serviced. My HVAC man was here to remove a fintube that needed to come out before the wall to the addition could be removed. Actually, Jim has looked at the boiler 2-3 times recently. He added 3 feet to the chimney because the addition changed the roofline. He thought this may have caused the spill problem.
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Jim is an outstanding one man operation. However, the material you all have given me will give us things to investigate.
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The most significant thing you all have contributed is that the problem is likely connected to the input to the boiler and not to the chimney.
Any attempts to find the problem without a draft gauge would be quesswork.The one at the top of the picture at http://www.nationalcomfortinstitute.com/members/products2.cfm?product_id=25&Cat=Carbon%20Monoxide,%20Combustion,%20and%20Safety%20Tools is very good.
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