cistern overfilling intermittently

[myidentitymycrisis]

My toilet fills up after flushing and stops correctly. Then I come back later and it has dribbled in more water to fill enough to overflow.
Sometimes this happens, other times it’s fine for days. I have to keep a bucket below but it doesn’t catch it all and floorboards are getting soaked.
Repairs have already replaced the whole flushing mechanism, (I live in a council property) -and I’m loath to call them out again because it will probably behave perfectly when they are there.
Is it possibly that this could have something to do with running the taps?

No

Open the cistern lid and show us what's inside it please.

Indicate which of them have recently been replaced.

Where does the overflowing water come out?

On the inside of the cistern the max waterlevel will be marked with a line. Where is the line in relation to the real waterlevel?

I think they replaced the whole blue part with the ballcock on, the hose that fills the cistern from the water pipe, and possibly the big bit in the centre (blue)

The water in the photo is it filled up and it then fills again up to about 2 and a half inches. First it drips from the hole on the right which is filled with a plastic cap but the rubber seal around that on the outside is slightly off. Then if it keeps on filling it leaks from the hole at the back centre.

Sometimes I’ve checked it’s fine, only to hear it start gurgling independently.

Thanks for looking

OK. When it overflows, it should overflow through the white plastic pipe on the right. If that joint is leaking it probably wants tightening up. But that pipe should be big enough to take all the overflow, the level should never rise high enough to reach the mounting screw holes in the back. Take some more photos of that overflow pipe please, close up, inside and out. perhaps it is blocked.

More modern flushing valves incorporate an overflow so that the water goes down into the pan. Your plumbers have used a more traditional type that relies on the overflow on the side of the cistern.

As to the overfilling, you see the upside-down blue cup. That's the float. The cup fills with air during flushing, so it rises with the water level and should press by a lever on the valve to cut off the water supply. The type you have is a copy of a Torbeck or Armitage Shanks equilibreum valve. A very good valve is some ways because it is very quiet. However it is prone to grit, dirt or scale jamming the small parts inside, which is probably what has happened in your case. I don't see scale so you are probably in a soft water area. Often dirt or rust in the pipes is dislodged when plumbers are working, so they are supposed to let water gush from the pipe before fitting the valve to wash it away. It is actually very easy to dismantle and wash out any grit, but unless you are fond of DIY plumbing I won't advise you to do that.

You can try gently tapping or pressing down the white lever where the stem of the float attaches, this will open and shut the valve and may make it temporarily seal better. You can also (gently!) screw the blue stem down so that the float goes lower. This will reduce the filling height and will make the float press harder on the valve if it overfills. An inch or so will do. It is essential that the float goes up and down freely and does not rub on the cistern or the flushing valve, which prevents it moving correctly.

As the parts in your cistern look quite new, I think it is a fitting error or grit, but if you show some more pics I can compose a short note that you can copy and send to the landlord or housing company. It will probably advise that the plumber should come back and rectify the work recently done.

Looking at the flush valve, it might be a Dudley. This is an expensive brand often used in rental properties because it is unusually quick and easy to service when worn. But I can't place the fill valve. It might be the same brand but doesn't look quite right. Can you see any names or numbers?

(this is for interest only, won't affect you)

Hi
The hole on the right which we both assumed was meant for overflow is sealed and always has been. The black rubber seal on the outside is a bit leaky so it sometimes drips from there. So I thought this system must overflow into the toilet pan. Is that what is doing when a small amount of water falls into the pan?
I’m adding some more photo’s, to show the big hole centre back which it leaks out of, that seems to be for fitting the cistern differently. Should that also be sealed?

I have just pressed down on the blue cup and now see how that activates sealing the valve. The blue cup is very close to the back of the cistern but not touching it. Will I need to do that each time I flush ? If I reduce the water level it fills upto, will there be enough in the cistern to flush? It seems to be set to fill exactly to the line.

I’m in a hard water area but the parts are all over new.
Sorry for all the questions, and thank you so much for your help.

Yes it is a Dudley 2 part,
The fill valve says WRAS approved product

OK. You have two faults

1. the fill valve is letting by (probably due to grit)

2. the Dudley syphon has been fitted to a cistern that does not have an overflow pipe
   (probably the original fitting was a different type that incorporated its own overflow pipe)

A skilled or experienced plumber would definitely have noticed (2)

(1) might be bad luck or it might be they forgot to flush through the pipe.

Neither of these can be blamed on you.

Thank you so much.
It is really helpful to be able to know what to tell them. Thanks again