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Oversize boiler BANGS on colder days

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#21 ·
Oversizing the exp. tank will not hurt anything. Water in a closed loop system will not steam at or anywhere near 190*. You gotta be a lot higher than 212*. At 12 psi your looking at around 240*. But please dont do that. 190*, unless your under radiated at 24* outdoor temps should be more than you need to satisfy t-stats. It sounds like thermal expansion , Buderus is a fine piece of eqiupment how oversized are you talking. What are the length of boiler cycles (how many minutes on how many minutes off)? What is gpm required by manufacturer through boiler?
 
#22 ·
Has he checked the draft hood and flueway(baffles, etc.) to see if there is a misaligned plate that moves when hit with high heat and moves again when it cools? Have you watched the pressure gauge during this sound? Does it burp at all? What calls for the circulator, zvalve or tstat? Is the unit set up to have the circulator and zone valve open on a call for heat with the burner riding off of the zone valve auxiliaries, or through a aquastat? Is the circulator running when the unit goes BANG? If not, has your installer tried running the circulator before, during, after firing to see if anything changes? It might be helpful to get a sequence of operation from the call for heat to the burner shutdown.

edit: Does the burner cycle during one call for heat? how long are the burner-on times?

[Edited by rimek on 02-24-2005 at 08:38 PM]
 
#23 ·
Mark any chance you could post some pics of your system it would help us diag your problem better. Here's a couple of ideas that I thought of... on the buderus g 234's the return port is MUCH diffrenet from the supply nipple port in that it mixes the water through a series of holes drilled in the distribution tube. Make sure your contracter used the proper tappings. Also, check if the circ pump has an integeral check valve that could be chattering. Is there any chance that htis could be a control noise or does it definetly sound like a mechanical issue? Where are you located?
 
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Discussion starter · #24 ·
Again, thank you everyone for your comments.

beenthere: Circulator is TACO 007-F5. 1/25hp. 3250rpm.

Sweet: can't find recommended GPM thru boiler. The manual shows a graph of 1.45 psi drop at 17GPM. Does that mean anything? G234x-45 is rated as 187in/154out/134IBR vs 95 by rule of thumb, 40 calculated, 60 conservatively calculated. The loss, of course, is for the whole house. The largest zone is only 850 sqft. It's rare that more than one zone calls at a time. Avg burner cycle is 6min to reach hi-temp limit, and that's only if the t-stat isn't satisfied in mid-cycle. Tonight, I've measured 3 full cycles at 4min. Is that short?

Rimek: Start-up sequence: T-stat calls; z-valve starts to open; when z-valve is fully open, circ starts; (if boiler temp is lower than diff) damper starts to open; when damper is fully open, igniter starts.

ktm: other contractors that I have asked to diag have commented on 'good' workmanship of installation. I don't hear any chatter from the circ or fittings. I don't believe this is a control noise. Since the BANG occurs consistantly about 60sec after burners ignite, and again (important) about 60sec after burners shut-off, even when t-stat is satisfied and circ is off, I think it's a mechanical expansion/contraction. Sitting next to the boiler, it sounds deep internal to the boiler. When looking for that circ model number, I got a real good BANG while my ear was next to the supply: high to the rear on the right.

Note: outside temp = 24F. 55 ft of baseboard in 850 sqft in main living zone on first floor. T-stat set at 69F. It took 11 minutes to satisfy t-stat. t-stat called again 20 minutes later. Again took 11 minutes to satisfy. Burners were on for 4 minutes each time. comments?
 
Discussion starter · #26 ·
I've used 2 heat loss software programs. One from Slantfin and one that I found on line. On first pass both programs calculated that I'm losing only 40MBTUH. Rules of thumb suggest that the house loses about 90-100 MBTUH. So, I re-worked the numbers trying to be more conservative:like R-11 insulation instead of R-11 plus the R-4 foam used with my new vinyl siding, and single pane windows instead of double. The calculation only increased to 60 MBTUH.

Which number do you think I should use?
 
#27 ·
Has anyone checked the gas pressure or the burner alignment ? is the flame hitting the bottom of the boiler or is it between the sections .Sounds like it is out of alignment.

A boiler can make steam, at any temperature depemdent on the pressure where the flash may be occuring. This is not your problem though. When this is seen on a hot water system it is usually at the inlet of an oversized and improperly piped pump, the symptom is that the pump will go through a lot of seals.

[Edited by fat eddy on 02-25-2005 at 06:18 AM]
 
#28 ·
I would say the boiler is retaining heat keeping the baffles
hot and when cold air hits them, its giving you the popping noise.

If you keep short cycling that boiler the way you are now,you can look forward to frequent part replacment,as well
as high gas bills.

People make claims that a boiler with mass should not have
a need for a buffer tank,but what happen to a boiler that
is way oversize and on top of that you have very small loads
that not only short cycle the boilers,but put stress on a circulator as well.

Sir, your boiler is crying out for a buffer tank.

[Edited by simpleman on 02-25-2005 at 07:20 AM]
 
#29 ·
4 minute burn cycles is way too short. I agree, a buffer tank should be looked at. If your HW heater is nearing it's life end, why not get a reverse indirect like a turbomax or Ergomax? THese tanks hold between 25 and 30 gals of boiler water with a copper coil for the domestic water to flow through. Kind of like taking a tankless coil from a boiler and sticking it in a thermos bottle where the BTU's won't fly up the flue. You have plenty of extra BTU's to make hot water for the house and now you have a BTU "batery" that the boiler will charge up and the zones and hot water coil will suck the heat out. The boiler should run for at least 10 to 15 minutes and then stay off longer until it needs to fire again.
 
Discussion starter · #30 ·
Fat eddy: I will ask the installer to check gas pressure and burner alignment. Could this also cause the BANG on cool-down? The BANG that occurs 60sec after the burners ignite sounds very similar to the BANG that I hear 60secs after burners shut-off. If the burner is out of alignment, then something is getting hot that shouldn’t? Or, something is getting hottER than it should?

Simpleman: isn’t the boiler supposed to retain heat? One of the BANGs occurs only 60 sec after the burner shuts-off. I agree with you about the short cycles: high fuel bills and early mortality.

So, the buffer tank is a place to “dump” some heated water, the object being to pull the unused heat out of the boiler?

Johnsp: so an indirect-fired domestic hot water heater could act as the buffer tank? But, it has to be the “reverse” style that you describe. It sounds like it’s not really a zone, but the zones will draw from it. So, it’s in series with the supply?

But, a forward style, would just be another zone, and unless someone is taking a shower, it’s not really an additional load on the boiler. Right?

How would the cost of an indirect-fired hot water with installation plus continued high fuel bills compare with “right sizing” the boiler?

Just as a sanity check: the BANGs seemed to be related to burner activity. How does the buffer tank help the BANG 60secs after ignition? Maybe Fat eddy is closer to the target with his alignment question?
 
#31 ·
That would be something worth checking if the burner is misaligned or overfired it can be impinging on the boiler instead of radiating through the flue section, I think it could make some hot spots and cause noise on startup and cool down.
 
#33 ·
sweet said:
Water in a closed loop system will not steam at or anywhere near 190*. You gotta be a lot higher than 212*. At 12 psi your looking at around 240*.
Click to expand...
I have seen more than one boiler flash steam with 180 deg & 12 psi.Think about this.If you have a poor water flow situation or air pockets & one tiny spot on the heat exchanger is cherry red.....Would it flash steam?Yes!!!
 
#35 ·
I under stand flash points on a HX. Making steam and flashing steam arent the same imho. If this posts boiler was makin steam, The original post would have read a whole lot different.
 
#37 ·
I had the same problem with a boiler our company installed in 2001. We originally install exactly same size as what came out, without checking exactly how much BTU's the actual radiation elements need. After a couple of years of complaints by homeowner, we initially fixed all the expansion of pipes against wood framing. I then realized that the noise is internal. I can actually feel the noise, which is called "Kettling" through the jacket of they boiler.THis boiler has four circulator zones.If yhe boiler is oversized you will have the problem with lack of flow through boiler. When this happens the boiler will short cycle, but it will also cause the water inside the boiler to boil. Because there isn't enough flow through the boiler water isn't being circulated fully through all parts of boiler, causing water that's not moving to overheat and cause the"Kettling" noise. 2 things can be done. First is the boiler can be changed to match what radiation actually installed in the house. Secondly, since the zones are not piped properly for the needed flow of and oversized boiler flow. Installing a bigger circulator won't solve problem if the piping can't provide enough flow. A bypass will need to be installed with a circulator and some type of flow control.circulator needs to run whenever boiler fires. Adjust flow control to achieve proper temp rise you boiler requires. A uncirculated bypass won't work.

Let me know if this helps
 
#38 ·
I had the same problem with a boiler our company installed in 2001. We originally install exactly same size as what came out, without checking exactly how much BTU's the actual radiation elements need. After a couple of years of complaints by homeowner, we initially fixed all the expansion of pipes against wood framing. I then realized that the noise is internal. I can actually feel the noise, which is called "Kettling" through the jacket of they boiler.THis boiler has four circulator zones.If yhe boiler is oversized you will have the problem with lack of flow through boiler. When this happens the boiler will short cycle, but it will also cause the water inside the boiler to boil. Because there isn't enough flow through the boiler water isn't being circulated fully through all parts of boiler, causing water that's not moving to overheat and cause the"Kettling" noise. 2 things can be done. First is the boiler can be changed to match what radiation actually installed in the house. Secondly, since the zones are not piped properly for the needed flow of and oversized boiler flow. Installing a bigger circulator won't solve problem if the piping can't provide enough flow. A bypass will need to be installed with a circulator and some type of flow control.circulator needs to run whenever boiler fires. Adjust flow control to achieve proper temp rise you boiler requires. A uncirculated bypass won't work.

Let me know if this helps
 
#39 ·
LinkMech

I agree but he has already posted that a loop was installed and the it is circulating. His boiler is large for his home but it still should not be making expansion and contraction noise, which is what I beleive it is and not flashing or steaming.
 
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