Hot Water Boiler - Knocking Noise

scottW

8 years ago, I converted an oil fired boiler to a high efficiency natural gas boiler. The systems has always worked fine. This year I started noticing a "knocking" sound coming from the boiler when it is heating the water.

Is it possible that there is air trapped somewhere in the system that is causing this?

Thanks for any help...scott

Alan(CaliforniaRadiant)Forbes

Sometimes

knocking is associated with improper heat transfer, i.e. the water isn't moving fast enough to pull the heat out of the heat exchanger. The usual culprit is air somewhere in the system (not necessarily in the boiler) or a bad pump.

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Pat Clark

Knocking Noise

This could also be a mineral buildup inside the castings causing hot spots that boil and create more air. If this is the case you may be able to correct it with a good boiler cleaner additive. We use Silver King #5 with great results to clean out the build up and we also add 1 qt to new boiler installs and each and every time we drain the boiler for maintenance we purge out completely and add another quart. Not only does this help prevent mineral buildup, but also has lubricant for the circulating pump (longer life of the pump).

Pat

hr

What type of boiler?

Cast iron, copper tube, condensing? A brand name could help us come up with ideas.

My crystal ball says low mass copper tube. Raypak, Laars, Lochinvar, RBI. Am I getting warm?

These are generally more flow sensitive than cast iron type of boilers.

hot rod

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scottW

Vailant Gas Fired Cast Iron

I checked my radiators and I don't seem to have any air in them. In the past when I would have air in the radiators I could hear water rushing by in them.

The boiler that I have is a Vailant GA92 Series, Gas Fired Cast Iron.