Toilet won't always fill automatically

[Surfing Bird]

In the last 3 or so months, my toilet won't always fill automatically when it is flushed. This is a recent situation after living in the same home for over 20 years. When flushed, the toilet will now often just flush and glug to a halt with no water entering the bowl. I discovered quite by accident that, in those cases, turning on the sink or bathtub faucet will activate the flow, which doesn't seem hampered or slowed down by any sort of buildup. What causes this to happen? Do I need a new valve unit? Thanks for any help.

[Nestor]

Surfing bird:

No, you probably need to just check what's happening in your toilet tank or replace the rubber diaphragm in your toilet's fill valve.

Your toilet fill valve will have a small hose that shoots water into the top of your toilet tank's overflow spout to refill the toilet bowl after every flush. I could be that this hose has been moved so that the water is now being directed into the tank instead of the overflow spout (where it would then flow into the toilet bowl).

Also, modern toilet fill valves are very sensitive to pressure. You see, the way modern toilet fill valves work is by using the water pressure itself to shut off the water flow into the toilet tank. That's because the rubber diaphragm controlling flow of water into the toilet tank will have your city's water pressure applied to BOTH sides of that rubber diaphragm. The difference is that one side will have a larger area exposed to that pressure than the other, and since Force = Pressure X Area, there will be a net force causing that diaphragm to press down against the seat where water comes into the tank.

So, typically, the area exposed to city water pressure will be larger on the top side of the rubber diaphragm than the bottom. That causes a net force holding the rubber diaphragm down over the seat through which water flows into the toilet tank, thereby preventing further water flow into the toilet tank. When you flush your toilet, the water level in the tank drops, and a mechanical linkage pulls out a plug on the "larger area" side of the rubber diaphragm, releasing the pressure on that "large area" side and ensuring that the city water pressure on the "smaller area" side of the rubber diaphragm is sufficient to push the rubber diaphragm off it's seat, and allow water to flow under the diaphragm into the toilet tank. Once that float rises again, that same mechanical linkage pushes the plug back into the hole on the large area side, the pressure on that large area side now builds back up to city water pressure and pushes the rubber diaphragm back down onto the seat, thereby shutting off further water flow into the toilet tank.

That system works well for (so far as I know) ALL toilet fill valves. The problem is that this system is very sensitive to dirt getting into your toilet fill valve's diaphragm area and causing the diaphragm to remain open when it should close, or remain closed when it should pop open.

I'd check that the "refill tube" coming off your toilet tank's fill valve is pouring water directly into your toilet's overflow spout first. If it isn't, that's the problem, and it can be corrected by simply adjusting the clip on the overflow spout to make sure water is being directed into that spout while the toilet is refilling.

If it turns out that's not the problem, then the next thing I'd try is to either clean the area around the rubber diaphragm in your toilet's refill valve, or to replace the rubber diaphragm in the refill valve and also remove any dirt you see in the area of the rubber diaphragm in the refill valve.

Since that rubber diaphragm needs to move entirely due to the pressure on each side of it, having any dirt on either side that can allow water to leak under the rubber diaphragm or over it is going to cause the toilet refill valve to malfunction.

Hope this helps.

[HayZee518]

ballcock

the toilet fill valve is called a ballcock. real old ones were made of brass or bronze. they used a plastic or copper float at the end of a brass rod that interfaced between the float and the ballcock. it was purely mechanical in nature. float up, a valve seat would close. the newer ones FLUID-MASTER is one of them operates off a cup type float and a linkage to the valve body. a quarter turn and you can remove the valve assembly and clean it out. just make sure you shut off the inlet water valve.