Overflow from main tank

[TheGoat]

I have a problem with the main tank in the loft, it appears to be dripping water out the overflow valve into the garden.
I was kinda hoping i could just get up and tighten a screw and be done with it.... Wishful thinking i know!
I came across the following link : http://www.diydoctor.org.uk/projects/cold_water tanks etc..htm

And in particular:
If an overflow pipe, either from your toilet cistern or from the roof tank, is dripping, and adjustment of the height of the ball arm does not cure the problem, the remedy will be to exchange one of the black rubber diaphragms, according to the valve you have, in the pictures and diagrams below. The water must be turned off and the operation is simple. The rubber diaphragms are available at most diy stores and plumbers merchants.

I could easily enough turn off the water, but what am i replacing it with - if i were to go to B&Q and ask for a rubber diaphragm i'd expect them to refer me to the local GUM clinic!

Any help much appreciated.

 

[Bahco]

Just change the whole ball valve ( part 2 one). Easy enought to do and only cost you about £4. Adjust the arm so that it cuts off the supply 2 inches from the overflow outlet if the tank is supplying your cylinder etc.

 

[JohnD]

You can buy a complete new ball-valve for a few pounds... you will find it easier and quicker to fit the complete assembly except the screwed tail... then you can take the old one downstairs, dismantle it on the kitchen table where you have plenty of time, room and light, and fit a new washer to it and then wrap it up and put it next to the cistern ready for next time.

Edited: Not fast enough