01:37PM | 11/09/04
Member Since: 11/08/04
2 lifetime posts
Recently, I started hearing "knocking" sounds from the water heater vent. It only happens when hot water is being used somewhere in the household. Is that something I should be concerned about? Thanks.


05:32PM | 11/09/04
Generally noise from the water heater are not a concern after you identify what is causing them. Up high by the vent the knocking is usually from back flow nipples. These have balls in them that prevent the hot water from backing into the piping. You may or may not have them depending on the make and model. You can put your hands on the silver nipples and feel the knock. This sound will occur whether the burner is on or not. It's the flow of water.

The most common source of knocking noise is gas bubbles coming up through the sediment on the bottom of the tank. This would occur after the burner has been on for a couple of minutes and may continue after the burner goes out. Knocking may also occur when cold water hits the hot in the tank. This happens if your dip tube has gone out.


11:02PM | 02/11/14
Member Since: 02/11/14
1 lifetime posts
I have purchased a new home and every time the hot water kicks on, I get knocking coming from the flue/ chimney of the hot water heater. My builder is telling me that it is a natural occurance with the flue/ chimney heating up and colling down that causes the knocking. I can understand that since the knocking occurs after the water heater (Gas) starts heating, and stops 10-15 minutes after the water heater stops heating. ( I assume the cool down period). This is my 15th house and I have never heard this before. Is this correct that it is the ventilation/ flue material heating and cooling, if so, why has it never happend in any other house, and how do I stop it? Change flue/ chimney material? It is so loud that it will wakse you up from a dead sleep because the chimney goes behind the wall in the master bedroom.


02:13PM | 08/07/15
I have the same issue. Were you able to resolve it? My flue is not accessible, as it travels between walls from the basement to the roof. I decided against a power vented water heater when I built this house due to my noisy power vent heater in my prior house. Not sure I did the right thing.


11:26AM | 10/17/16
I have the exact same problem. Has anyone discovered a solution?
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