Why Are My Pipes Knocking - T-Tees - Your Answers Await, Life's Questions Unraveled

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1. Knocking happens only while hot water is running

Common scenarios:

A clicking/knocking noise starts soon after a hot water tap is turned on
Clicking/knocking noise doesn’t stop until several minutes after the hot water tap is off

Most likely cause

Poor construction of CPVC water lines. Some homes use CPVC (chlorinated polyvinyl chloride) as their hot water supply pipes (i.e., the pipes that deliver hot water to your shower, sinks, washing machine, etc.). Now, if a CPVC line was routed through a hole or area that is too tight, you’ll hear a rubbing/clicking/knocking noise anytime hot water runs through that pipe.

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Why?

Well, CPVC piping naturally expands when hot water runs through it. To accommodate this behavior, a plumber should make sure that CPVC piping has plenty of free space around it at all times to prevent friction. If it’s lodged in a tight area, you’ll be stuck with the annoying knocking noises.

You’ll know that poor construction of CPVC water lines is your issue if:

You see cream-colored or light tan piping running to your hot water appliances. These pipes will also be marked “CPVC”.
You only hear the knocking/clicking noises when a hot water tap is turned on
The noise stops several minutes after the hot water tap is turned off

Refer to more articles: Why Does My Tea Taste Like Water

What’s the solution?

The only solution is to find the CPVC pipe(s) that are causing the noises and give it more “breathing” space (i.e., room to expand without rubbing any surrounding materials).

Because this could involve cutting into walls and/or relocating CPVC piping, we suggest you leave this job to a professional plumber.

2. Knocking happens after a cold or hot water supply shuts off

Common scenarios

Pipes in your bathroom wall are making a knocking sound every time the toilet is flushed.
Knocking noise happens in the laundry room when the clothes washer finishes filling.
There’s a loud banging noise in the water pipes when the sprinkler system turns off.

Most likely cause

Water hammer. While many people incorrectly use the term water hammer to mean any loud banging in your pipes, it’s actually a specific phenomenon.

A water hammer occurs when a water valve is suddenly shut off. All the water that was running then crashes into the valve, shaking your pipes, creating the knocking noise you hear.

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Category: WHY