The fill valve on my new toilet guts shuts off instantly if the water supply knob is turned on all the way. FYI my knob only turns a quarter turn to have the water on all the way.

It literally shuts off within one second of flushing and obviously no water fills the tank.

I have to shut the water supply valve under the toilet off and back on part way to get the toilet to fill. When the water shuts off I also get the hammer sound. I have tried two different fill valves in two days and the same thing occurs with both.

The modern style float is not even touching the water as the toilet might get 100 ml

The type of valve is the kind with no ball float, its the new style

  • What is the model # of the toilet (if the toilet is new) or of the "guts" (if it is an old toilet with new "guts")? Jan 4, 2019 at 5:18
  • It's a 6 year old toilet with new guts. The guts are a brass craft bct015
    – franco c
    Jan 4, 2019 at 15:44

1 Answer 1


I've had a similar problem and it was due to an "Auto Burst Detecting" supply line.

Something similar to this: http://media.wattswater.com/F-FloodSafe.pdf

The high flow of water is "Detected" by the FloodSafe line. This causes it to trip and shut off the line as it thinks the high flow of water is caused by a broken line. My solution was to just leave the valve partially off and live with the long toilet fill times.

Note: Leaving the valve partially off will most likely defeat the purpose of the FloodSafe line (As it cannot have high enough flow to detect a burst line).

  • Should I go back to old school ball float cause it takes forever to fill with water low
    – franco c
    Jan 5, 2019 at 0:45
  • No! The old ball floats are, in my opinion, junk compared to the modern stuff. What you got (brasscraft btc015) is similar to the typical Fluidmaster replacement kits. I have also used (currently in 2 of my toilets) a new type "Next" by Danco, which I like, but YMMV. Jan 6, 2019 at 0:16

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