I just finished replacing a 10-15 year old ballcock-style toliet fill kit with a new Fluidmaster 400AKR complete repair kit. I have used this kit in 2 other bathrooms in the same house with no problems at all. This time, however, I noticed strong water hammer DURING toliet fill (not at the time of valve cutoff). Reducing incoming water velocity at the toliet supply has stopped the hammer but the toliet tank fill time is unacceptibly slow (3-5 minutes on a low-flow toliet).

I have owned this house since construction in 1999 and have never had water hammer issues of any kind prior to today's events. I am on city water and to the best of my knowledge, my main supply line pressure regular is working as intended. I am familiar with water hammer when a valve closes abruptly, but have never heard of it occuring during fill.

Any advice is appreciated!



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Water hammer occurs when the flow stops, not while it is moving. The noise is probably a loose washer(or broken piece of one) in your supply stop. It can vibrate and make a lot of noise.

KCRoto, thanks for the reply. I have a couple of follow up questions regarding your answer.

(1) What is the likelihood of the fill valve intermittantly opening and closing (chattering) during fill, creating a water hammer effect? I have watched the flow into the tank and believe it to be streamlined (laminar) during fill so I don't have any evidence this is happening, I am just searching for another cause before tackling the next issue...

(2) I assume that to replace my toliet supply stop, I will need to turn water off at my house main. Can you confirm that this is typically the case, or is there typically an intermediate shutoff valve elsewhere? I ask because my basement is finished and the house supply valve is in a difficult-to-reach area that will require some effort to get to; I might be able to get to an intermediate valvle easier than the house supply valve.

Thanks for the help and advice!

Depending on your area and how it is plumbed, you may have a curb stop, a stop at the water meter, and an entrance valve into the house, and possibly a second valve after the entrance valve. It is worth the effort to find your main water shutoff in case of emergencies anyhow. Usually, the water in urban residential homes enters through the front of the house, and there is almost always a hose spigot directly above it. If I walked to your front door and needed to shut off the water and your basement was finished, I would look for an access panel or closet built in that area if I could see nothing else. The chances of of another whole house shutoff valve are slim, but you could start at the cold side of the water heater and work backwards. If you find a valve in the line that is somewhere before the water heater, you can shut it off and try it; you could get lucky, but don't hold your breath. As a side note, I recommend changing more than just the toilet stop if you are doing it, and replace all the toilet stops with 90 degree turn angle/straight stops as appropriate.

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I ask because my basement is finished and the house supply valve is in a difficult-to-reach area that will require some effort to get to;.....

You need to correct this issue ASAP - you may need access QUICKLY one day !

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