Concealed Cistern. How to fix or Change the system
Concealed Cistern. How to fix or Change the system
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Discussion

chukwe

Original Poster:

215 posts

130 months

Saturday 2nd August 2025
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We moved to our current house (5 years ago) where the downstairs toilet Cistern is concealed and the only access I could find is the small cabinet under the sink as shown in the Photo.

In the past 2 months, filling up the cistern has become very slow and takes around 20 minutes to fill up.

How can go about fixing this? Anyone has experience with this kind of Concealed Cistern? I'll like to know my options before calling a plumber.

Thanks

mdw

413 posts

295 months

Saturday 2nd August 2025
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Check that the tile above the top of the toilet sn't held in with silicone if it is cut that out and that will be your access panel. If it isn't and is grouted then it was installed by an idiot who assumed it would never need accessing.

JoshSm

2,848 posts

58 months

Saturday 2nd August 2025
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Slow fill might (if it's like the ones I had put in) be blockage at an valve inlet filter insert rather than a problem in the valve itself.

Though equally it might just be a tired valve sticking.

Either way you still need to get in which on that looks like it would be through the top as it doesn't have a panel type flush as access.


chukwe

Original Poster:

215 posts

130 months

Saturday 2nd August 2025
quotequote all
mdw said:
Check that the tile above the top of the toilet sn't held in with silicone if it is cut that out and that will be your access panel. If it isn't and is grouted then it was installed by an idiot who assumed it would never need accessing.
I check it few weeks ago when I saw something similar on YouTube, but there's none. I just took pictures of the Top and the bottom cabinet







alangla

6,134 posts

202 months

Saturday 2nd August 2025
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I had a similar problem, if anything mine was initially better and got worse. You’re not going to like the answer.

I had a hatch on the top and was able to get into the cistern and get the top off it. The cause of the slow fill was that the diaphragm on the fill valve had aged and wasn’t opening fully. Replacing it got the fill rate up and solved the problem.

The “getting worse” bit was that soon after, the diaphragm on the bottom of the syphon failed, meaning it wouldn’t flush at all. To fix that I had to get to the bottom of the cistern and that proved almost impossible. The concealment was plasterboard with small tiles, so I initially tried to get the grout out with a view to cutting it. That failed and I ended up going at it with a circular saw. There are shrapnel marks on the wall now where bits of ceramic got ejected from the saw. Managed to re-attach my new access hatch using a couple of repair plates and tile grout, so it looks ok. Also fitted a demountable syphon so next time it’s 2 clips to get to the diaphragm.

In short, you’re fked. Either accept you’re going to be cutting to get to the cistern or budget for a new bathroom. If you do get another fitted bathroom, make sure it’s one where the panelling around the cistern is removable.

All this over a part worth literally pennies.

Sorry to be the bearer of bad news

chukwe

Original Poster:

215 posts

130 months

Saturday 2nd August 2025
quotequote all
alangla said:
I had a similar problem, if anything mine was initially better and got worse. You re not going to like the answer.

I had a hatch on the top and was able to get into the cistern and get the top off it. The cause of the slow fill was that the diaphragm on the fill valve had aged and wasn t opening fully. Replacing it got the fill rate up and solved the problem.

The getting worse bit was that soon after, the diaphragm on the bottom of the syphon failed, meaning it wouldn t flush at all. To fix that I had to get to the bottom of the cistern and that proved almost impossible. The concealment was plasterboard with small tiles, so I initially tried to get the grout out with a view to cutting it. That failed and I ended up going at it with a circular saw. There are shrapnel marks on the wall now where bits of ceramic got ejected from the saw. Managed to re-attach my new access hatch using a couple of repair plates and tile grout, so it looks ok. Also fitted a demountable syphon so next time it s 2 clips to get to the diaphragm.

In short, you re fked. Either accept you re going to be cutting to get to the cistern or budget for a new bathroom. If you do get another fitted bathroom, make sure it s one where the panelling around the cistern is removable.

All this over a part worth literally pennies.

Sorry to be the bearer of bad news
Does yours have a cabinet at the bottom like mine? I'm thinking someone may have access to Cistern from there

alangla

6,134 posts

202 months

Saturday 2nd August 2025
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No, it was a hatch on the top and that was it. You could get onto the top of the cistern, but there was no access anywhere else.

The flat I had previously did it right, the entire casing around the cistern was held on with wing nuts so the whole front panel came off and you could get all round the cistern, that’s how it should be done, but no-one does it.

alangla

6,134 posts

202 months

Saturday 2nd August 2025
quotequote all
Looking at your photos again, the grout on some of your tiles looks a bit odd. If you were to de-grout the horizontal one above your pan, would it lift out?

Regbuser

6,162 posts

56 months

Saturday 2nd August 2025
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Multi tool with a thin grout blade will remove all the joints to the flat capping tiles above the pan, then hopefully they'll lever off (gently) giving to you access to the water inlet isolation valve thence the flush valve - good luck !

Little Lofty

3,767 posts

172 months

Saturday 2nd August 2025
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Concealed cistern but exposed sink plastic trap confused
I also think that top tile might come off, the push buttons set into an access panel are far better than those small things.

Simpo Two

90,778 posts

286 months

Saturday 2nd August 2025
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The little door is nasty and the join between the basin and back is a mess. Given the cistern problems would this be time to rip the lot out and start again?

I fitted Grohe concealed cisterns 20 and 22 years ago and they're both still working fine.

Inbox

1,337 posts

7 months

Sunday 3rd August 2025
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Stick your phone in the access door to take some pictures, might reveal something, typically there would be some lift out panels for access.

Can you get any replacement tiles?

Wacky Racer

40,423 posts

268 months

Sunday 3rd August 2025
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What idiot thinks of these ideas just to make the bathroom look "nice?"

At least design it for easy access in case of an issue, same in Premier Inns etc.

The_Doc

5,887 posts

241 months

Sunday 3rd August 2025
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I begged and bartered with my wife not to do a concealed cistern, or worse still a wall-hung cistern in our new bathroom.
We did one in the last house refurb and it's just pain when it goes wrong. And it will go wrong.



We now have this, with valves accessible.

Sorry to hear your pain, OP, prepare to chop it open and then re-tile, at worst.
At best lift up the tiles above.

Use AI camera services (Google Lens etc) to track down new matching tiles

Edited by The_Doc on Sunday 3rd August 08:47

Cow Corner

680 posts

51 months

Sunday 3rd August 2025
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It s perfectly possible to build a concealed cistern with sufficient access - (our houses previous owners thankfully did ours with both a removable top and a fancy timber decorative front panel, which conveniently lifts off to expose the system) - the problem is that , based on years of surveying and dealing with defects in residential property, many installers are just idiots.

Edited by Cow Corner on Sunday 3rd August 09:06

Panamax

7,764 posts

55 months

Sunday 3rd August 2025
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The reason for that little wooden door is very obvious - someone had to break in to sort out a plumbing issue because there was no access. Sound familiar? They broke the tile in the process. You can see what's been pit back is two cut down remnants of the old tile.

I suspect in rsality you're going to have to cut/smash through the top in one way or another. It would be a good idea to think about replacing the whole top surface with something new and better looking, for instance a piece of granite made to size. Othervise a new row of plain coloured tiles. If you can salvage an unbroken tile or two in the process you could devise something much tidier than the small wooden door at the same time.

Chumley.mouse

855 posts

58 months

Sunday 3rd August 2025
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If you cant find any replacement tiles, then an option is to remove the top tiles and replace with some kind of top. An off cut of composite worktop or something like that. Maybe a similar colour ?

One way or another your going to need to get into it.

Simpo Two

90,778 posts

286 months

Sunday 3rd August 2025
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Chumley.mouse said:
If you cant find any replacement tiles, then an option is to remove the top tiles and replace with some kind of top. An off cut of composite worktop or something like that.
In the fresh light of dawn I say rip it out and start again with something nice - and an half-inset basin!

The contrivance is already a bodge, it doesn't need more bodges on top.

miniman

29,079 posts

283 months

Sunday 3rd August 2025
quotequote all
Simpo Two said:
In the fresh light of dawn I say rip it out and start again with something nice - and an half-inset basin!

The contrivance is already a bodge, it doesn't need more bodges on top.
I concur, any opportunity to tear out that bodge job should be seized.

andy43

12,373 posts

275 months

Sunday 3rd August 2025
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Flush plate every time. Geberit systems are ace - you can remove everything via the flush plate if you need to.
This… it’ll be painful. Maybe adding a hockey stick piece of upvc as a new shelf ‘feature’ might cover up what you’re going to have to do to those tiles…