banging boiler

[Deleted User]

I have a Weil-Mclain PD-5 hot water boiler, 80,000 BTU output that is aprox. 32 years old. Aquastat is set to maintain 180 degrees, which it does. Boiler pressure is 12-14 psi. The problem is that after the zone calling for heat is satisfied, the burner and circulator shut off and the boiler itself bangs. It is a problem I noticed that started last year. Nothing new has been done to the system. In the 30 years I have been in this field, I never ran into this problem (Proof that even tho we are in the field, we are not exempt from problems occuring at home). I was thinking of replacing the boiler to a slightly larger and more efficient one (1800 sq. ft. house---boiler has a hard time mainting even 68 degrees on a 0-10 degree day even when I boost the aquastat to about 195. I may need additional baseboard also) I am really worried that the banging is the boiler expanding and may loosen the push nipples or crack a section. Anyone ever run into this? Thanks

kevin coppinger_4

the boiler could...

be flashing to steam...what is the pressure?the aquastat could be inaccurate and overshooting...are there any signs of leakage? I think the weil had o-ring so that should give flex between sections....Let me ask as to keeping up...did you do a heat loss? is there enough baseboard? how much on each loop/zone? don't just upsize w/o it.
Many times if you addinsulattion to walls,windows and the basement piping you can boost performance. kpc

[Deleted User]

banging boiler

Thanks Kevin for the reply...
Boiler pressure is 12-14 psi on a known accurate gauge. Aquastat is accurate also.(Water would have to be over 243 degrees before it flashed to steam). There are no signs of leakage. House is 20 by 30 feet, 2 floors plus a finished basement. Active baseboard is installed on all perimeter walls on the 1st and 2nd floors (kickspace heater in the kitchen). Basement has 17 ft. baseboard...no problem heating that area as it is 80% below grade.
90% of house is insulated and attic has R-30 installed.
Heatload calculation was done by local supplier but, I may need a little more baseboard in the living and dining room areas due to 6' bay windows in each room that were added later and not figured into the original heat load. Do you think a B&G series 100 circulator can handle aprox. 250-300' of piping if all zones call at once or should I put a bigger pump in? (Right now, there are 4 zones with Honeywell zone valves and 1- Series 100 pump).

kevin coppinger_4

what is....

the length of the longest loop? W/o doing the math it should do fine. Is that baseboard all fin, no dummy ,cover only baseboard? When the heat loss was done that took into account all that wall factors...r values? If the entire primeter is baseboard there should be more than enough to handle the design load w/ 180f water.Something is not adding up...I might get a second opinion on the heat loss.

[Deleted User]

Hi Kevin
All the perimeter baseboard is full fin...no dummy sections. Loop is aprox. 140' from the boiler and back. I limit the flow to the 1st floor with a ball valve on the 1st floor return to try to send the flow to the 2nd floor and get more heat. I think I need to add insulation to the piping and add additional baseboard to the 1st floor.(Some of the baseboard is blocked by furniture). I ordered the Slant Fin heat load program and will try that out when it arrives. The banging boiler thing still makes wonder, whats going on.

kevin coppinger_4

from what info...

you have posted I roughly figure 53000 BTU fro the house... if the output of the boiler is 80000 as you say the boiler is plenty big enough...is that # the D.O.E. or the I=B=R number for output? Zoning might help here..a couple of zone valves...or 2 circs. Grundfos or Taco.
How cool/hot is the return water to the boiler? That is a ton of baseboard for 1- 3/4" loop.... kpc

[Deleted User]

to Kevin

There are 4 zones. 1st and 2nd floor zones, a 17' basement zone and a small kitchen zone supplying a kickspace heater.
1st and 2nd floor zones are the largested with aprox. 140'each of total piping. (aprox. 90-100' active baseboard on the 1st and 2nd floor zones... all fin) Not sure what the TD is across each zone.

kevin coppinger_4

the max # of ft.

of baseboard(600 btu/ft.) on a 3/4" line is 67'+/-...for a 20F delta T.