Geberit toilet - water trickling into basin

[Whatsername123]

Hi everyone,

I have a Geberit cistern concealed in a wall, for a while now we've had a slight trickle into the basin. It seems to get worse then calm down randomly.
After thorough research I followed instructions yesterday and removed the flush valve and fill valve and checked for the following problems:
- limescale build up: wasn't that bad, cleaned off what was on both parts anyway as per instructions in YouTube videos before re-assembling.
- silicone seal faulty at the base of the flush valve: Cleaned this, there were no water blisters in ours and it looks good as new. This sounds like the most common cause of our problem however ours seems to be working fine? Could it still be faulty?
- adjusted the fill valve so water fills up to 6L. Goes over slightly the first time I refill after turning the water back on, however after that it fills to the normal level .

When we flush the toilet and the tank refills, it seems to be fine for about a minute - no tricking. Then the water starts trickling into the basin. Looking, it looks like water is continually leaking out of the tube at the bottom of the fill valve (the tube which has Geberit written down the middle).
Does anyone know how I could fix this?
I hoping I'm describing it okay, I'd be happy to take pictures or film a little video demonstrating the problem.

I spent 7 hours fiddling with the problem yesterday, trying all the instructions online and troubleshooting based on common problems described in this forum - no luck! I'm really hoping someone might be able to help.

Thanks in advance!

 

[Ian]

Welcome to the forums @Whatsername123 . If you've got photos of the setup, that may help.

Funnily enough, I had an identical problem and posted about it here a while back: https://www.diy-forums.com/threads/geberit-concealed-cistern-leaking-into-pan.287831/

Did you check the underside of the seal for blisters? The top of mine looked good as new, but the bottom was problematic.

Is there anything blocking the flush valve mechanism? (grit, dirt, toilet cleaner tablet residue, etc...)

If you push down on the unit when it's in place, does that stop or slow the leak?

 

[Whatsername123]

Thanks Ian!

Thanks to your advice I might just have inadvertently found the problem and *holds breath* fixed it!

I pushed down on the unit to test the leak, and it was still leaking. I thought I'd take it apart one last time to triple check the silicone and randomly there was another piece floating in the tank which hadn't been there before - like a plastic cage the bottom of the flush valve inserted into (I just thought the version of the unit didn't have one, as it looked slightly different to other valves on YouTube), it looks like I just hadn't pulled it out when dismantling it all these times.
This part had black silicone ring which WAS covered in limescale... a quick clean and its now working.

So relieved... a plumber was quoting £150+ this morning!

Thanks again for your help. At least nowI know the anatomy of my toilet, I feel experienced enough to deal with any problem it might get in the future.

 

[Ian]

Good work! That's an easy £150 saved now .

 

[Silentrunning]

Welcome to the forum @Whatsername123