Inside you will see its a very, very basic design with what is effectively a bicycle brake cable from the push button unit, pulling on a little pully device which lifts the plunger at the base.

Unfortunately some moron has completely blocked in the back of the toilet (as it looks good, until something goes wrong. It wasn't clear to me if I could simply remove the top half of the old cistern valve, and replace it with this new one so I took the plunge (pun intended).

this is the cistern with the top off and you can see where the wire comes through and goes between those 2 white bits of plastic(which are cylindrical) but i can't work out how it holds it together? Thank you for your reply, that's a lot of company name changes in three years, the one I have is marked up 2008 when it was still Macdee! I have a dual flush button and cable, bottom fill valve in my cistern and it occasionally sticks open allowing the water to continue to drain out the cistern. It is quote new, we moved in around 8 months ago and I would say it's only been done in the last year or so. Is it possible that there is a cast recess in the bowl into which a nut sits, so that the cistern can be attached/detached purely from above?

The top section of the valve is compatible with the now discontinued AFV40100 and AFV40200 models and simply fits into the existing cradles without removing the cistern. It's 2014 and the problem still occurs and WD 40 still works, but just make sure you have a good look at the layout of the little plastic box before you take it apart! The plunger on my flush has gone "tits up" and i have taken it apart to find that the wire has detatched inside the cistern, now, i can't see how to retatch the wire!

I will let everyone know how I go on, may be a useful guide for anyone with a similar problem in the future.

Faulty or damaged toilet fill valves can cause a toilet not to function properly and can waste water.Please note: Purchasing the replacement valve will require the removal of the complete valve assembly. Further, if this doesnt solve your problem, at the other end of the cable is the actual valve mechanism.

I then sprayed a load of WD40 onto the guide rails and the pully mechanism and then pulled on the cable repeatidly to get the WD40 to move around and do its buisness. turn the valve 1/4 of a turn will dismantle the top of the valve from the base so you can gain access to the seal at the base.

I then used a pencil to poke down the same hole and wiggle the small blue lever until it happily sprung back cleanly again. Use the tools cog symbol on your camera/phone/tablet to set the smallest image size, then post a picture. I give this 3 stars because I bought one in October 2019 (as the one that came installed with our bathroom about 5 years previously had broken - plunger mechanism was jamming so water was continually flushing into the bowl) but it has only lasted until August 2021 - with the same problem.