Water Heater Knocking When Toilet Flushed

[Mike Lamb]

A one bathroom ranch on a slab. This knocking sounds like it is coming from the water heater and only happens when I flush the toilet, not when I run other fixtures.

???

https://www.youtube.com/v/WPntL4XrPBI

[Raymond Wand]

Its likely a bad valve on the fill mechanism of the toilet. The diaphragm could be resonating due to water pressure, thus the noise.

Did you try closing down the shut off valve to see if it affected the noise.

[Darrel Hood]

This description also raises the possibility that the toilet is using hot water. If so, there is an opportunity to save a little money.

[Steven Turetsky]

A one bathroom ranch on a slab. This knocking sounds like it is coming from the water heater and only happens when I flush the toilet, not when I run other fixtures.

???

https://www.youtube.com/v/WPntL4XrPBI

Change your diet.

[Mike Lamb]

A hot water feed to the toilet makes sense. I never felt the tank to see.

[Ray Babcock]

A hot water feed to the toilet makes sense. I never felt the tank to see.
I've come across this noise when the water shut off valve is not opened competely. Also some homes don't have water hammer chambers.

[Mike Lamb]

A gentleman at The Inspectors Journal suggested that it is likely the ball in the WH heat trap knocking around when there is a slow water feed from the WH tank to the toilet.
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[Ray Babcock]

Down here in the south we plumb the toilet with the cold water supply. Is there a reason to run a hot water pipe to a toilet?

[Mike Lamb]

Down here in the south we plumb the toilet with the cold water supply. Is there a reason to run a hot water pipe to a toilet?

It's not common but it can stop toilet sweat and I have been tempted to do it to a bathroom at a summer home I have in Michigan. The condensation can be a real mess.

[Raymond Wand]

It would be easier to switch the toilet out for a new one with a lined tank. Why pay to heat water to stop sweating?