Plumbing help: toilet cistern inlet valve won't shut off

My toilet flush mechanism has a design like this one: https://www.screwfix.com/p/fluidmaster-bottom-entry-fill-valve/84007

Recently, the inflow of water has not completely shut off even when the water level has raised the float sufficiently to do so.

I took the system apart and replaced the washer that looks like this:

But this hasn’t had any effect. Even when I lift the arm to the maximum to press down and close the valve, water still escapes. Does anyone know if there is anything else I can try short of replacing the whole unit? I’ve watched lots of YouTube videos on this but they are all about replacing the valve at the bottom of the cistern to prevent leaks from there into the bowl, and that isn’t my issue. I’m trying to do this as cheaply as possible as we plan to replace the whole bathroom next year, but we need it to last a few more months first.

Replace the entire mechanism. At least here in the US, it would cost about $15 or $20 at a hardware store.

Amazon has the complete kit for $12:
https://www.amazon.com/Fluidmaster-400CRP14-Universal-Flapper-Toilets/dp/B007TUHQWY

Or you can get just the fill valve for $7:
https://www.amazon.com/Fluidmaster-400A-Anti-Siphon-Universal-Toilet/dp/B00002ND6R

Thanks, I figured that was what I’d have to do, just wondered if there was another way because access to the screw at the bottom of the cistern isn’t easy and I probably don’t have the right wrench for the job. Might have to give in and pay a professional to do it.

I don’t know what the plumbing secret is to just replacing the washer but I ran into the same problem enough times that I don’t even bother with it anymore. It’s not worth my time trying to figure it out. I don’t know if something wears around the washer or gets warped but the time trudging back to the store for a whole unit negates any money saved. I’ve had enough late night calls from friends for help on leaking toilets that I just keep one of the units on-hand.

This is a trivial repair. Just make sure the water supply is off and the tank is empty. Disconnct the water supply. Ordinary tongue and groove pliers (Channellock, e.g.) will turn the nut on the bottom of the tank holding the fill valve assembly in place. You don’t need to unscrew anything inside the tank. Don’t overtighten the rubber washer when you put in the new assembly.

Agreed, assuming you have decent clearance around the bottom of the toilet, this is pretty simple. By far the trickiest part of this job is removing the supply tube from the old tank valve assembly without damaging it beyond use. Time will tend to freeze these connections and they can be incredibly stubborn to remove without destroying them.

Start this repair first thing on a Saturday morning. If it goes right, you’ll be done in ten minutes. If it’s stubborn, you’ll have time to make 1-4 runs to the hardware store to buy replacements before they all close.

This turned out to be the issue - unlike the YouTube video I watched, the nut under the cistern that I need to loosen to remove the ballcock mechanism is recessed, so I couldn’t access it. I had a couple of pokes with the pliers but couldn’t come close to shifting it. So, plumber it is. On the plus side, I also removed, cleaned, and refitted the flush mechanism while I was in there, and not only does it still seem to function correctly, I think it’s stopped a slow leak between the cistern and bowl.

Praise be! The problem now seems to have mysteriously fixed itself. Not for long, I dare say, but if it could last us six months that would be tremendous.

Hey, take the win and flow with it.

How long had the valve been leaking prior to your attempts to fix it? It’s not impossible* that a small bit of mineral scale flaked from the inside of the supply line and lodged itself in the toilet valve assembly preventing it from closing. Your actions may have dislodged it from the valve seat and returned it to normal function.

  • I wouldn’t bet money on it but stranger things have happened.

If the nut is recessed there are plumber socketsjust for this situation if you need to get to them in the future. They’re not expensive and much cheaper than a plumber.

If you have iron pipes it’s common for rust nodules to break loose and make their way to these types of valves causing them to leak.

Only a few days. We have modern pipes but very hard water so could have been a bit of limescale. The odd thing was that I spent quite a bit of time fiddling with the mechanism and turning the water on and off to no avail. Eventually I put it all back together and turned the water off. Then when I put the water back on a few hours later, it stopped filling as normal. Weird.