Toilet cistern water level slowly increasing

hatt55 · 21 April 2019 at 7:02AM

I have a push button toilet flush and yesterday it broke - the base of the button sheared away from the button itself. Its a cable type one, so I thought everything from the cable onwards was ok and spent a few hours going between plubing merchants trying to buy a new button only but without success. In the mean time the lid has been off the toilet cistern and I've noticed that although it fills to what appears to be the correct height initially (it can still be flushed just using the cable without the button) it seems to continue filling very slowly afterwards. Overnight the water level has gone up by a few centimetres - not enough to trigger any overflow yet, but it has continued filling.

This may well have been happening before - as the button is attached to the flush mechanism via a cable I haven't really taken the cistern lid off until now. The mechanism has played up a bit in the past but this has tended to be immediately after a flush and I think the cable gets a bit stuck so a little bit of water continues to drain. That can be remedied by flushing slightly more water. I remember one instance where water started running into the pan without warning and in hindsight perhaps that was the overflow kicking in.

Just wondering if anyone has any ideas of what this might be before I think about replacing the whole mechanism (or getting a plumber to do so - I'm nervous of water related DIY!)? There are lots of suggestions on the internet for the level in the cistern being set incorrectly or it refilling rapidly, but I can't find much information on this slow filling.

I can try and add a photo later if that helps.

nofoollikeold · 21 April 2019 at 11:02AM

There are two main components inside a toilet cistern, the inlet or fill valve and the outlet flush valve or syphon.

Because your WC is push button operated, it is most likely that the outlet valve is the flush type, which means the valve is lifted off its seating at the bottom of the cistern to let the water flow into the pan. Syphonic outlet valves are usually handle operated. You push the handle down, it lifts up a piston which sucks water into a syphon, water comes out of the syphon and continues to do so until the cistern is (nearly) empty.

The inlet valve is attached to the house cold water system, mains or tank fed. The valve is attached to a float, which rises on the surface of the water as it fills the cistern. When a predetermined level is reached, the float shuts off the in flow of water and the level remains the same until the WC is flushed.

It sounds as if the inlet valve in your cistern is letting a small amount of water flow by, even when it is supposed to be off. Inside the valve there is a rubber "diaphragm" washer which actually stops the flow. These can get hard over time, and fail to seal completely, allowing water past.

If you are lucky, there will be an isolation valve in the pipe bringing water to the cistern (the valve will be outside the cistern). Turn this off, which usually means having a screwdriver slot at right angles to the pipe, flush the toilet, and make sure it doesn't refill. Remove the diaphragm and get a replacement from a plumber's merchant and fit the new one.

Alternatively, replace the whole inlet valve, they are not very expensive.

If you post a picture of the cistern internals, and of the broken flush mechanism, you may be able to get more help from the forum.

hatt55 · 21 April 2019 at 8:35PM

Thanks for the explanation - very helpful.

I think your description basically describes what I have. Here is a photo for completeness:

Unfortunately I don't have an isolation valve on the inlet pipe (indeed, since I moved in I haven't been able to find the main stop valve in the house and can only turn the water off via a shared supply pipe in the street. It's on the list for if I ever take the hall floorboards up and get access to the pipe!).

Given that the flush mechanism is also not quite right, I feel like it might be a job for a plumber to get it all in working order and install an isolation valve in order that I can try and tackle this in future if necessary. I'd like to have a go, but I fear it might take me quite a while and the neighbour's water would have to be switched off for the whole time.

nofoollikeold · 22 April 2019 at 12:13PM

Can't be completely sure but looks like a MacDee DVE 0600 inlet valve and MacDee DVA 0100 flush valve. You can get new diaphragms for the inlet valve, look at https://www.toiletspares.co.uk/dve0600-bottom-entry-float-valve.html

If there is sufficient pipe length (at least 3" / 75 mm straight) exposed, it could be frozen and an isolation valve fitted.

If you are not sufficiently confident to do it yourself, it shouldn't take more than about an hour and a half for a plumber to isolate, fit an isolation valve, and change both inlet and flush valves. Caveat: Provided there are no issues like like of access. Most plumber won't just change the diaphragm because there are so many different types it often requires a trip to the merchants mid-job, and ends up costing more. If you are in London, expect to pay about £150 plus VAT for parts and labour, less elsewhere.

Toilet cistern water level slowly increasing

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