Replacing flush mechanism in the loo

[Mendeleyev]

I'm hoping that someone can give me some advice to get started on this (or make me get a plumber in!) Our loo is leaking through the overflow to outside. I want to make it stop. The arm the ballcock is on is not returning to a high enough position to completely stop the valve from letting water in, resulting in a slow drip through the overflow. I have found a replacement I think on screwfix here but before I start dismantling the loo! is this an easy job to do? How do I turn the water off to the loo? Is it easy to get a seal and no leak? Thanks in advance for any advice, even if it's get a plumber in.

If you have an isolator where the water pipe meets the valve you are to fit, you turn the screw head to cut off water. Sometimes there is a flexible hose shrouded in mesh with sometimes a built in isolator. Again turn the screw head to cut off the water.The next thing is bail out the water in the cistern as it will go on the floor . Use a big car wash sponge.
The seal washer has to go inside the tank. Be careful not to cross thread when tightening up the pipe to the inlet valve as its only nylon and will cross thread easily .

Thanks for the advice. I found a good YouTube video that takes me through what I need to do. I now know where the main stopcock is, but I will look and see if there is an isolator valve.

Before you do that, is the ballcock or the arm it's on adjustable? You might be able to move it so that it cuts off the water inlet at a lower water level, i.e. before it overflows.

is the old one brass or plastic?

does the water supply pipe enter the cistern through the side or the bottom?

I've had a look at the old one and can't see any way to adjust it. It does have some screws but if I mess with them it just drips more. It keeps dripping unless I hold the arm with the ball cock up. It just seems to be sagging and so not shutting off the clave properly. If I hold the ball cock arm up, it stops the dripping.
It is a bottom entry valve and it's plastic. About 17 years old.

Hmm, a photo might help. Generally ball cocks have some way to adjust them as this is a normal part of fitting them; ours lets you partially unscrew the float or adjust a little plastic screw that presses against the inflow mechanism.

I would say you have had your monies worth out of the old one. I would replace the diaphragm and siphon too, that's more complicated as you the cistern has to be removed from the pan. If I could see the type you have it would help. The siphon lifts the water and is only a sheet of thin plastic that forms a seal in order to lift the water. If the inlet valve is worn then the diaphragm wont be far behind it. Two bolts hold the cistern to the pan and if they have corroded badly you may need some mole grips to remove them.

I forgot to mention in my first post regarding the inlet valve, wrap about three thickness of ptfv tape round nylon thread first. This tape costs about a pound a roll and stops water getting past the threads .

About three years ago I only paid about 60 quid in B&Q for a new toilet unit and about a fiver for a new soil pipe seal from a plumbers shop.
It was white and even included a toilet seat. The kit even included the two stainless steel screws that fix the pan to the floor. It was the button operated type with any excess water going not outside but down the pan.

It did crosst mind to just get a new loo roneik but unfortunately it's not a white suite but cream, so a bugger to colour match. Think I'll buy the stuff and have a go!

Buy a new bottom entry half-inch Fluidmaster WC cistern filling valve. Get the one with the brass shank as it is less easily damaged. Have a look on the Screwfix website and see how the price compares. £15 is good. You do not have to take the cistern off the pan.

If you ever do have to take the cistern off, fit a new flushing valve and doughnut washer. It will be hard work because the fixing screws will yave rusted solid. I prefer a Flapper flush valve if you can get one.

The only modification to the plumbing was a new braided hose and cutting off a bit of the pipe to adjust for length. You don' need any skill it's just common sense a hacksaw or pipe cutter adjustable spanner and one hour to do. Save some money and whatever you decide do it yourself.

I never touch central heating but general plumbing with compression fittings either plastic or metal have allowed me to fit bathrooms and kitchens in several houses . It's all a matter of thinking it out. I can solder but find with braided hoses and compression fittings easier unless it's somewhere that the pipe is on show.