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I wouldn't lose sleep over this, except the unexpected and fierce sound startles my girlfriend and cat every time.

So I just replaced the refill valve on our toilet (using a kit, so everything from the lock nut to the overflow spout, but not the plunger or handle). It works great. No signs of leaking (at least not on the floor or walls). It does a full refill every time right up to the refill line printed on the back of the tank. The overflow spout is above, not inside, the overflow pipe.

Every so often (maybe once an hour), the toilet shrieks for a half-second, like the float drops just enough to cut on the flow and then rises with just a squirt of water.

My first thought was evaporation, but 1) I'm surprised it's that sensitive and 2) I know our old fill valve didn't do this (at least I don't remember it doing it, and I'm sure both gf and cat would have mentioned it if it did).

The one thing I didn't tweak was the water level screw, because the critical point line and overflow pipe were the specified 1 inch apart (eyeballed) and the water fills to exactly the above-mentioned line.

If it is the water level, is this spontaneous and short burst indicative of needing to lower or raise the water level? And can someone explain why it happens at all? I imagine the water-level adjustment changes where the float "floats" so if the water level is where it should be after a refill, why would it run 30-60 minutes later for a short burst?

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+1 Shrieking toilets? Startled household? Full blast refill? You, sir, have a flair for the dramatic. –  Steve Jun 4 '13 at 6:47

3 Answers 3

up vote 14 down vote accepted

The most common problem that causes the symptoms you describe is a slow leak around the flapper. A very small amount of water drains into the bowl over time, lowers the tank level a slight amount and activates the float valve of a couple of seconds to refill the tank. What you should do before getting carried away dissecting the fill valve, is to check the flapper, clean it and it's seat well and be sure it is centered on the drain. If there are any signs of wear or cracks around the edges, replace it. Monitor the tank level between phantom fills, does it change at all? The second thing is to slightly lower the float so the water fills to apx 1/2 inch below the fill mark. This will eliminate the possibility that you may be losing water over the overflow, and tripping the fill valve.

These checks are simple, cheap and often solve a very common problem. Good Luck.

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Good call. It was the phrase "toilet shrieks for a half-second" that made me think of excess pressure on the inlet. –  ChrisF May 11 '12 at 10:54
    
I was thinking of replacing the flapper anyway, but hesitated for fear that they aren't standard in width (or hinge). As far as the water entering the overflow pipe, would that happen 30 minutes after the refill finishes? –  Anthony May 11 '12 at 10:59
    
Some of the new valves are very touchy, especially the ones with the float riding on the ballcock assembly. Depending where it is set, it may only take an 1/8 of downward movement to activate. If it set too close to the level of the overflow tube, it could happen. I'm betting on a worn or misaligned flapper first. –  shirlock homes May 11 '12 at 11:57
    
I lowered the level, still got it, but seemed less frequent. I replaced the flapper--as mentioned before I was already thinking about it-- still happened. Lowered the level another notch, haven't noticed it since. Thanks! –  Anthony Jun 1 '12 at 11:32

Did you fit the flow restrictor (usually a plastic helix) that fits inside the supply pipe?

It could be that the water pressure is too great for the valve and it forces it open. This relieves the pressure enough for the valve to close again. It's not enough to cause the the water to overflow and when you use the toilet during the day it will keep getting reset to the correct level.

One way to check this would be to flush the toilet last thing at night, mark the actual water level and then see if it's slightly above that level in the morning.

If you no longer have the restrictor that came with the valve, or can't find a replacement, you can get restrictor valves that you could use instead.

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Is this similar to the flow restrictors in showerheads and sink faucets that I can't wait to pop out? Would it go before or after the washer? Are they a standard size for a toilet supply pipe? I'm pretty sure there either wasn't one or I discarded it (foolishly) while replacing the fill valve. If the size is standard, I'll just pick one up. –  Anthony May 11 '12 at 10:38
    
@Anthony they should be standard, about 1 - 1 1/2 inches long. I can't remember exactly where it should be fitted (it's a while since I fitted our toilets/refill valves). I'm fairly sure it's just after the isolation valve. I'll try and dig up an image. –  ChrisF May 11 '12 at 10:40
    
They sometimes slide up inside the new valve depending on the type of restrictor, good pick-up @ChrisF –  UNECS May 11 '12 at 10:49
    
If it slides up in the valve, it was pre-slid, as I didn't do anything other than put on the shank washer and connect the overflow nozzle. If it is in the supply line (and at the coupling point), I don't see one but I'm also not finding any good hits on google for getting a replacement. Will try lowering the float a notch since that's free. –  Anthony May 11 '12 at 11:06

Add a few drops of food coloring into the tank after it has refilled before it kicks in again. Mix it up a bit to make sure it is dispersed. Then watch the bowl to see if any of that colored water leaks though. If so, then you know for sure that you have a leaky flapper as others have described. If not, then the issue is probably on the supply side.

Note, you might want to lower the level temporarily, just to make sure any of the colored water doesn't go down the overflow in the case the supply is putting the water in and it is not leaking.

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great tip. I forgot to mention that. Works great. +vote –  shirlock homes May 11 '12 at 16:59
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You can also shutoff the water supply. If the level drops, you know you have a leak. –  BMitch May 14 '12 at 12:16

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