Pipes Knock..is it air or expansion.

Old 11-21-06, 06:36 AM
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Pipes Knock..is it air or expansion.

We have hot water baseboard heaters and everytime the furnace kicks in, the pipes in our bedrooms knock. It's quite loud at night and wakes us up.

What is this caused by...air in the pipes or expansion?
Any advice is appreciated.
Old 11-21-06, 07:38 PM
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Some sound, usually described as a "crinkling" sound, is normal.
Banging or knocking sounds are not. Since noises are hard to troubleshoot in person & almost impossible on the web, I suggest you contact a service person well versed in hot water heat to come in, listen, & see what he/she can do.
Old 11-22-06, 06:25 AM
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I have the same thing. At times its bothersome especially in the morning when the boiler kicks on. My baseboard radiators start poping. To me it sounds like the aluminum fins are expanding. A friend thinks its air. I've heard air in the lines and its a loud banging. I just live with it since it has happened since I moved in.

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