Dudley 88 - cistern still filling?

[Colin78]

I've got a Dudley 88 turbo syphon. Its been working fine up until recently. The tank is filling to a higher level than usual and keeps on taking in water and the overflow trickling into the bowl.
I can clearly still hear the water running through the pipe into the tank. I've shut off the water supply for now as its just running water through.

Could this be an issue with the float? Are there any other possibilities?
Any help would be appreciated for a novice

 

[terryplumb]

Is the float moving freely ? Flush the cistern and manually pull up the float arm. If water doesn't stop coming into the cistern ,replace the whole valve ,with a fluid master brass shanked one.

 

[Colin78]

Yes the arm is moving and lifting when at the correct filling level but it continues filling higher.
I did lift and hold the arm right up manually after flushing (when the tank was low) to see if it stopped but it still continued filling until overflowing into the bowl.
Thanks!

 

[terryplumb]

Replace the valve .

 

[Colin78]

Will do.
Have sourced this one

https://www.screwfix.com/p/fluidmaster-bottom-entry-brass-shank-fill-valve/47792

Thanks for your help!

 

[terryplumb]

There is a seal that may need to be replaced ,where the valve meets the supply pipeworks fitting. Depends on how yours has been plumbed in ,there are different methods. Seal could be a 1/2 inch fibre washer ,or could be a rubber washer. Can you post pic ?