Leaking Grohe Toilet - Concealed Cistern

[Marcello]

Hi guys

Hope you can help on this one. 

We have a concealed Grohe toilet cistern - I don't know exactly which model, as it was already installed when we bought the property, but is likely to be similar to the one in image 1 - attached.

It has developed a small leak - water leaking slowly into the toilet pan, meaning the cistern is having to fill up every 2-3 minutes.

 

When I researched this, everything I found pointed to needing to change the Outlet Piston (image 2) - as this can deform and fail over time.  Changed it - still have the leak. 

So then I bought a new Flush Valve Assembly (image 3) which comes with another Outlet Piston already fitted.  Still had the leak. 

And so finally bought a new Flush Valve Seat (image 4) - but still have the leak. 

 

Upon further investigation I think the leak is that the Flush Valve Seat is not forming a seal at the bottom of the Cistern (image 5) - as when I open the tap to allow only a small amount of water into the cistern, it immediately leaks through to the pan.  

 

The outlet hole at the base of the cistern is clean, free of any limescale or other deposits.  Any suggestions?  It seemed a simple fix at first, I don't want to call a plumber out if I am missing something simple. 

 

Thanks in advance!

 

 

[Marvin]

Sorry this was missed...

 

Two reasons the water can run:

 

The filler valve (part 37905) is not sealing off properly causing the tank to fill to high causing the water to rise over the overflow level and empty in to the pan

 

The seal on the flushing mechanism is not sealing completely causing water to trickle through into the pan.

 

These things often happen in hard water areas when there is no softener device.

 

If your on a meter, keep isolated when not in use.

 

Good luck 

 

M

 

 

Edited August 26, 2021 by Marvin

[Temp]

Is the water level set too high on the float? eg so it's filling up too much and going down the overflow?