Pipe shudders at water heater after toilet flush

[Rph52G]

I looked around, but couldn't find my problem in this forum. Once a month or two or so, after flushing the master bath toilet (Toto Drake with newer interior parts) I hear a loud banging coming from the water heater cold water pipe outside. It goes on and on, so I have to turn off the house water supply. That fixes it every time. All other water outlets work fine and never bang. I went under the house and checked the pipes to be sure they were strapped down. They are, but the plastic braces near the water heater had torn loose from the wood. I re-secured using metal braces. The house is all copper, but the pipes under the master bathroom are 1/2" while the rest of the pipes are 3/4". I'm not so sure the problem would be solved with a water resistor. The water heater is about 5 years old. The old water heater didn't have this issue, although we did have water hammer from the kitchen sink. That was solved by replacing the "steel nipple" at the water heater water supply intake. After the new water heater was installed we didn't have problems with the toilet flush until about a year ago.

UPDATE Feb 6, 2019: On his recommendation, I had a plumber secure the pipes to the wall where they emerge from under the house and reach up to the top of the water heater, about 4 months ago. We haven't had any shuddering since. Case closed.

 

[Reach4]

If you are getting some kind of sound or vibration only during the toilet refilling, I would replace the fill valve.

If you want to experiment first, try closing the stop valve, on the supply line to the toilet, part way to see if the sound changes.

 

[Sponsor]

 

[Rph52G]

If you are getting some kind of sound or vibration only during the toilet refilling, I would replace the fill valve.

If you want to experiment first, try closing the stop valve, on the supply line to the toilet, part way to see if the sound changes.

No sound issues from the toilet itself during and after flush. Fill valve works properly. Sound is loud banging caused by water pipes shuddering near water heater.

 

[Jadnashua]

Are you saying that it only happens when flushing that one toilet, and not from any other water use in the house?

 

[Terry]

No sound issues from the toilet itself during and after flush. Fill valve works properly. Sound is loud banging caused by water pipes shuddering near water heater.

That could be the fill valve on the toilet causing water hammer as it ends it's fill. If the pipes can move and the shock arrives, they can bang.
Some fill valves shut off smoother than others.
One other cause if the pipes are shuddering during the fill, is a loose washer in the shutoff to the toilet. I open the shutoff at the wall all the way and then turn it in a little. If it's mainly closed down with a worn of loose rubber washer it can flutter causing the hammer.

 

[Rph52G]

Mostly certain it's only this one location, although a slim chance it's caused by the hall toilet as well.

 

[Rph52G]

That could be the fill valve on the toilet causing water hammer as it ends it's fill. If the pipes can move and the shock arrives, they can bang.
Some fill valves shut off smoother than others.
One other cause if the pipes are shuddering during the fill, is a loose washer in the shutoff to the toilet. I open the shutoff at the wall all the way and then turn it in a little. If it's mainly closed down with a worn of loose rubber washer it can flutter causing the hammer.

That sounds intriguing. It's a Korky silver top model 528. I'll close the shut-off valve a little to see if that helps. Shut-off valve was installed in 2007, so not that old. It's attached on an old galvanized pipe stud. I was thinking about having the stub removed and finishing off with copper.

 

[Jadnashua]

After 11-years, you may need to replace the cap seal on the Korky fill valve. It's about $3, takes no tools to replace, and shouldn't take more than a few minutes. The seal may be worn out so it doesn't work well, plus, there could be some rust crud on the mating surfaces from the galvanized pipe in the supply line. Depending on water chemistry and supply pressure, I find in my home, I have to replace the seals about every 4-years or so.

 

[Rph52G]

The Corky fill valve is a year old. I replaced it when I replaced the leaking seal between the water tank and the toilet base. It took a long time to figure that one out.

 

[Reach4]

The Corky fill valve is a year old. I replaced it when I replaced the leaking seal between the water tank and the toilet base. It took a long time to figure that one out.

If you came to suspect the fill valve, you would replace the Korky R528CM Replacement Cap Assembly for Fill Valve.