loud knocking

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Posted by Domenic on March 03, 2001 at 21:28:32:

I have a Repco residential boiler that is around 30 yrs old. I live in a split-level house. The piping system for the base board heat is split into two zones. I have lived in this house for the past 5 years. In that time I have replaced both (Honeywell) zone valves, drain valves, and the overflow release valve. At times I have been able to reduce the knocking in the system to to almost nothing. Last winter in particular, after flushing the system a couple times and securing the pipes in the basement,it was a very quiet season. However, this winter it is making a lot of noise again. It does not seem to be related to any specific point in the heating or circulation cycle. For some reason, it happens more in the early hours of the morning - every ten minutes or so. The pressure remains at 12 PSI, and temperature is 180 when running.

What is causing this banging? Is it an abrupt change in the water pressure? Is it pockets of air being pushed around in the system? Are the pipes fastened to the ceiling too tightly, without enough room for expansion?

I have gone through every room in the house and tried refasetening any loose baseboard pipes to the pre-existing brackets. I have also tightened up any play in the loose pipes so that they don't have room to bounce around and bang against the wall. This has worked, but occassionally I have to repeat the process.

The biggest problem has been in the basement. All the copper pipes are bracketed tightly to the rafters. Some have gray foam pipe insulation around them so that they should at least be more muffled even if they did bounce against the wooden rafter.

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