Performance Series Fire
Why does my new boiler make the pipes bang when the unit kicks on?
I just had a new boiler installed known as: The Prestige Excellence Series combined with a High Efficiency Condensing Stainless Steel Wall Mounted Gas Boiler with a built-in “Tank-in-Tank" Indirect Fired Water Heater. 3 honeywell zone valves were used with the installation. Everytime the heat kicks on, I get a rumble from the pipes and a loud bang. Certain rooms I can hear the water flushing through until it warms up. I strapped down every pipe including the baseboards and it still hasn't helped. When the unit kicks on and I'm standing in front of the boiler, it sounds like a fast surge of water and then I hear the rumble in another portion of the house. I have turned the circulator pump down to the lowest performance and this has not helped. My plumber has bled the lines twice and it still happens.
I was told by an hvac guy that my boiler is oversized....could this be the problem? Any responses would be greatly appreciated.
Mpfffff.... Here are a few things it could be and places to start:
a) You must have an expansion tank. If it is of the old-fashioned sealed-air type, it must be drained every so often to make sure that there is enough air inside to handle the expansion. If it is a bladder-type, make sure it is properly pressurized. That will depend on the number of stories in your house and the size of the system. If by some odd chance you do not have an expansion tank, that would explain everything you describe, Get one installed ASAP - and make sure it is correctly sized for your system - and make sure that all your zones are connected to it.
b) Do you have an air-purge fitting? If there is air in the system, you will get all sorts of banging and turbulence that will cause all sorts of noises. And air can get into the system from any number of sources including poorly installed bleeder valve and similar conditions.
c) It is very nearly impossible to oversize a modulating boiler sufficiently much to cause the system to boil water, and at the same time it is very possible for even a correctly sized unit to boil water if the controls are not properly set. So make sure the limit switches and any supply/return water sensors are correctly set and/or installed.
d) If the entire system is new, and incorrect fittings were used, or the system was installed poorly, you could be getting turbulence. This is very nearly impossible to cure altogether, but you can greatly reduce it by making sure the operating pressure is correct and that there is no air in the system. Your operating pressure should be around 10 pounds (2/3BAR) _cold_, and up to 15 pounds (1BAR) for a house over 2 stories.
e) If you are on a loop system (not a 2-pipe system), you need to provide an expansion-loop to allow for pipe movement for each long run of pipe. DO NOT try to 'tie down' your pipes or you will get much more violent movement when expansion does happen. When copper is heated it _does_ expand, and it _will_ move. The only question is where and when. Better you know and control where and how.
Designing a hot-water heating system is almost as complicated and time-consuming as installing it - and further to this it is almost a lost art. But if the basics are addressed, you will be fine.
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