Clanging Boiler on start up

gfrbrookline

My boiler makes two loud of clangs within 20 seconds of firing from cold. It's a Burham V904A with a Beckett gas burner. I don't think it could be a water hammer in the pipes because all of the pipes are cold and there is no air moving through them since the boiler water is cold.

Is this likely just the thermal expansion of the boiler or should I be concerned?

Fred

Pictures of the near boiler piping would help us help you. Not likely thermal expansion if it is cold. If it is hot enough for expansion noises, it is hot enough for steam to be hitting a pool of water, maybe in the header. Do you have an equalizer and is the header pitched towards it so that water doesn't pool in the header?

gfrbrookline

I know the A dimension seams short but it is actually 23" from the water line. The take off is 4". I will agree before anyone says anything that the installer should have used 2 take offs from the boiler. They wanted to reuse the header, if I knew then what I know know I would have had them scrap it and install a drop header.

Fred

WOW, a lot to try and see there. Is this a counter flow system? It looks like the mains are lower at the boiler than they are as they travel away from the boiler, but I also think I see where a dry return comes back to the boiler and then drops to the boiler.
If it is a counter flow, I don't see any drips, into a wet return, right after where the mains connect to the header. That is likely your problem. If it is suppose to be a parallel flow and each main has a dry return at the far end of the main that drops, at some point to the floor and enters the boiler, then the installer pulled your mains down to connect to the header. That is a problem as water would run back down into the header

gfrbrookline

It is actually a parallel system, two mains, 75' each. There are dry returns on each end as well as two returns for the step risers that tie together about 4" above the floor. The main vents are at the end of the dry returns about 18" before they drop down to wets because there is no access to the end of the mains since they are above a finished ceiling in the basement unit. The hartford loop is textbook.

The boiler also has a hot water loop for the basement unit that feeds off a heat exchanger and two feeds off the back of the boiler that heat two 80 gallon DHW indirects. It sounds like a lot but it works quite well, we have had this set up since 2005 without issue.

The vaporstat, mercury, is set to run between 14 and 6 oz confirmed by a 1-3psi gauge and it rarely ever runs more that one cycle.

You can see the amount of main venting I have. The radiator vents are a mix of Gorton No.4, No.5's, 1 No. 6 on the largest radiator in the farthest unit from the boiler and several Ventrite #1's in the two units directly above the boiler. The 10K sq. ft. building with 7 units is balance within 1 degree, it took me years and many fights with unit owners but everyone is happy now.

Fred

So where does the bangs seem to come from? From the actual boiler or from a pipe near/around the boiler? It should not bang.
It's not the flue damper is it?

gfrbrookline

Here are pics of the returns turning down to wet and the hartford loop.

gfrbrookline

The flue damper is fixed or at least it appears to be. I have a draft enducer on top of the chimney that kicks on right before the boiler fires, but the clang seams way to loud to be coming from the draft pipe. It doesn't sound like it is coming from the boiler or the header. It doesn't make sense for it to be coming from the header since there is no velocity coming out of the boiler when the water is still at 160 degrees.

It is colder today and the boiler has kicked on twice since I have been home. It still makes the clang but with the pipes being warmer between cycles it is much quieter and on the last cycle only clanged once at start up.

Fred

Is it from a pump or check valve on the hot water loops?

Jamie Hall

I'm suspecting an expansion noise very near, but necessarily in, the boiler. These can be very hard to track down. If it should happen that you are next to the boiler next time it fires up, you might be able to locate it better. Might even put a hand on the header and see if you can feel it kick when it clangs, for example...

gfrbrookline

Sounds like the way I use to tune my old car. It's amazing what you can figure out with a long screwdriver. Too bad the younger generation can't figure anything out unless you can plug it into a computer.

gfrbrookline

@Fred the clanging only happens when the boiler fires for steam.

Fred

I suppose it could be one of the side panels or the top panel on the boiler that pops in or out as it warms up???

gfrbrookline

I lowered the water level by an inch and all quieted down. I am guessing the lines he drew on the site glass were too high and water was collecting in the header? The level is much closer to the boiler manual now but I suspect my feeder may be mounted a little high.

gfrbrookline

That worked for a few cycles but the banging came back. Ripped the insulation out on the runout and found a reducing coupler on a section that is almost flat. Looks like I have to wedge two radiators on two floors up to give it a little pitch.

Any suggestions on which order I should go in?

Each radiator has its own riser off the runout. The first riser is a 1" the second is 1.5". The fist riser goes straight up, the second has an 18" pipe that goes 45 degrees before going verticle to the riser/radiator.

Jamie Hall

Reducing coupling? Not the world's best idea Eccentric, flat side down? Or concentric? If the latter, and the pitch is flat, it could well have enough condensate trapped to occasionally get "caught" by the steam and bang...

Fred

I don't think you will eliminate that problem until you either eliminate the reduction, on the horizontal run-out or add a drip at that location that drops into a wet return.

gfrbrookline

@Fred I was thinking I could tie into a dry return. I have a Parallel system with a section, the one that bangs, that feeds 3 radiators that turns into counter flow.

@Jamie Hall the feed off the main that is almost flat goes from 2"

Jamie Hall

Is it a true dry return you are talking about? In which case you'd need a trap. Or is it a "dry return" which is really an extension of a steam main? If it's the latter, tying into it may create some interesting flow patterns -- and may not help much.

Your mention of mostly parallel flow, with the banging section being counterflow, could be problematic. Where does the condensate from the counterflow -- banging -- section go when it gets to the parallel flow section? Can it go anywhere at all? That counterflow section is going to need good pitch -- at least the 1" in 10' and more if you can get it.

gfrbrookline

sorry didn't finish.

It goes from a 2" main a 90 elbow to a T with a 1" riser to a 2-1.5 reducer to a 90 elbow at 45 degrees that goes vertical after about 18".

gfrbrookline

Here are some picks to help understand my problem.

gfrbrookline

The flat or level section is the one in the middle that has a 2" to 1.5" reducer with a T built in, so a 2", 1", 1.5" coupler.

Fred

You have a one pipe system, you can't tie back into the dry return (as @Jamie Hall says) an extension of the main. That will just feed steam into the drip. It needs to go into a wet return.

gfrbrookline

@Fred I have a parallel system so my returns are mostly dry returns. Why couldn't I treat this section the same as the other drip returns I have from the step in the building and perhaps tie into one that is about 10" away.

Fred

@gfrbrookline , I guess you are going to have to better describe what you are calling a dry return. If it is an extension of the main, after the last radiator run out, that will still carry steam and the system can't distinguish a drip from another radiator run-out. Steam will flow into it and hit the water that you are trying to drain away from the horizontal reduction. You will just move the hammer from the reduction location to the drip location.
Having said that, if you have a true dry return, separate piping from the main and a trap that prevents steam from getting into it. You can do what you suggest.

gfrbrookline

@Fred it is a "dry return" as @Jamie Hall has suggested as an extension of the main which carries steam back to the boiler. My mains are vented on the end of the returns before they drop down and go truly wet.

gfrbrookline

If I can raise the two radiators that feed off the relatively flat pipe an inch or so it should correct the pitch problem correct? I think I may be over thinking this solution. Since it will be pitched it will also overcome the reducing coupler although since it is conical and not bell shaped I am not sure it would hold water.

Jamie Hall

gfrbrookline said:

If I can raise the two radiators that feed off the relatively flat pipe an inch or so it should correct the pitch problem correct? I think I may be over thinking this solution. Since it will be pitched it will also overcome the reducing coupler although since it is conical and not bell shaped I am not sure it would hold water.

Might do. worth the try...