Grohe Concealed Cistern - Very very slow weep into pan

[steveoelliott]

Hi,

 

I have a 1 year old Grohe concealed cistern which appears to have a very slow weep into the pan when not in use. I already checked the level is not near the overflow and both the fill and flush valve have been replaced. The only thing that hasn't is the little cage at the bottom of the cistern that the flush valve pushes into but I'd be surprised if this was the culprit given there are no moving parts to this.

 

Now when I saw weep, it is hardly noticeable. I don't even see a drip but it does show on toilet paper if the pan and the area where water enters the pan comes into contact with it.

 

My question is, should this be bone dry a couple of hours after the last flush? Is it normal to have a slight weep?

 

Thanks in advance.

[Mr Punter]

I have found that they all leak.  I have used several makes.  We are in a hard water area so it may be the scale that kills them.  Just had to refund over £100 to a tenant because she has said her water bill is high due to a leaky cistern.

[steveoelliott]

3 minutes ago, Mr Punter said:

I have found that they all leak.  I have used several makes.  We are in a hard water area so it may be the scale that kills them.  Just had to refund over £100 to a tenant because she has said her water bill is high due to a leaky cistern.

Well, mine is under warranty from Grohe so I could defer to them to fix it but it might just not be fixable. 
 

My Thomas Dudley concealed cistern downstairs also has a very slight weep, but that’s much older

[steveoelliott]

@Mr Punter So Grohe came back to me and they are going to send a senior engineer to look at it. They mentioned removing the pan but I can't see why they need to do this and how it will help. Given that the pan is not Grohe and has been in place for over 10 years, I am reluctant to let them touch it and will refuse. IMO the issue with weepage can be troubleshooted from the cistern. You can imagine, what would happen if something went wrong and the pan got damaged, leaked later etc.

Edited July 3 by steveoelliott

[Nickfromwales]

If you take the flush valve out, then look at the lowest point, you should see the soft rubber seal. Take that off, turn it 180^o and then put it back on. This should be sufficient to sort the water passing the seal.

 

It's on the Geberit website / vid's as their '10 year' maintenance or something....

[steveoelliott]

7 hours ago, Nickfromwales said:

If you take the flush valve out, then look at the lowest point, you should see the soft rubber seal. Take that off, turn it 180^o and then put it back on. This should be sufficient to sort the water passing the seal.

 

It's on the Geberit website / vid's as their '10 year' maintenance or something....

Thanks. I don’t suppose you have the link handy?

[Nickfromwales]

58 minutes ago, steveoelliott said:

Thanks. I don’t suppose you have the link handy?

It’s basically a short video just showing exactly this, remove flush valve, switch the rubber around, and refit. 
 

Same vid for the different models iirc. 

[steveoelliott]

Thanks @Nickfromwales

[saveasteading]

I did the turning over and regretted it.

Mine is Roca.

I removed the rubber washer, cleaned it, reversed it and refitted.

What was a strong trickle was improved to a slight trickle. It could be stopped by jiggling the flush to give it another chance to reset.

So I bought a new washer and it's fine now.  

It wouldn't be a big deal but it's such a fiddle fitting in there....and I dropped a very particular  connecter in and lost it.

(Expanding plasterboard plug to the rescue).

My ongoing concern is that the washer 'mates' with an outlet that may get mucky with lime but is unreachable.

[Nickfromwales]

I only fit Geberit tbh, just bloody bombproof stuff tbf, and I have never had a call-back. 

[steveoelliott]

6 hours ago, Nickfromwales said:

I only fit Geberit tbh, just bloody bombproof stuff tbf, and I have never had a call-back. 

Are they the same as Grohe? I know Hansgrohe are.

Edited July 4 by steveoelliott

[Nickfromwales]

2 minutes ago, steveoelliott said:

Are they the same as Grohe? I know Hansgrohe are.

No, a totally different brand.

 

LINK

[steveoelliott]

To circle back on this, Grohe sent another "senior" engineer out. They wanted to remove the pan which I refused as if it went wrong, it would put us in a awkward position. He did show me pictures of pans which hold water near the flush pipe entry which gradually leak into the pan. He did empty the cistern and demonstrate they water was slowly trickling into the pan so this theory does stack up. For good measure he replaced the bottom seal anyway. What will be interesting is leaving this for a few days without use (like when going away) and seeing if the weep eventually stops.

[Nickfromwales]

On 08/07/2025 at 16:15, steveoelliott said:

He did show me pictures of pans which hold water near the flush pipe entry which gradually leak into the pan. He did empty the cistern and demonstrate they water was slowly trickling into the pan so this theory does stack up.

That is a thing, but usually caused by the flush pipe not running downhill, eg it wasn't cut short enough so there is a trap of water that then sits in the horizontal bit between the bend and the pan.

 

On 08/07/2025 at 16:15, steveoelliott said:

What will be interesting is leaving this for a few days without use (like when going away) and seeing if the weep eventually stops.

Agreed, and will be the decider. Don't forget that for this to be a true test you need the cistern full of water, so there's weight on the seal, so don't empty it and isolate the feed.

[steveoelliott]

8 hours ago, Nickfromwales said:

That is a thing, but usually caused by the flush pipe not running downhill, eg it wasn't cut short enough so there is a trap of water that then sits in the horizontal bit between the bend and the pan.

 

Agreed, and will be the decider. Don't forget that for this to be a true test you need the cistern full of water, so there's weight on the seal, so don't empty it and isolate the feed.

I would do food colouring but it will stain the plastic cistern no doubt

[Nickfromwales]

10 minutes ago, steveoelliott said:

I would do food colouring but it will stain the plastic cistern no doubt

Easy tiger, let's not go all Mary Berry on this lol. Just leave it for 72 hours and check to see if there's still a constant dribble.

 

If not, then bake a cake to celebrate.

 

[steveoelliott]

2 hours ago, Nickfromwales said:

Easy tiger, let's not go all Mary Berry on this lol. Just leave it for 72 hours and check to see if there's still a constant dribble.

 

If not, then bake a cake to celebrate.

 

Although we have other toilets, it’s the one in the main bathroom and we have young kids so will have to be when we get back from holiday later in the year LOL